View Full Version : Of course, we must talk about Hardness

08-17-2007, 04:20 AM
Introduction To Hardness

Defining "Hardness"
The term "hardness" causes lots of confusion in ponding circles. Everyone knows that koi like "hard" water, but very few seem to know what hardness really is, how to measure it, and how to change it at will. Fortunately for us, many areas of the United States are blessed with moderately "hard" water. Given the wide tolerance of koi and this gift of natural hardness, many ponders get along splendidly without knowing what hardness really is just by performing occasional partial water changes and maintaining a low bioload. If you live in a soft water area, maintain a heavy bioload, or have frequent heavy rains, hardness is a measurement you need to know.

Two Hardness Numbers
Authors Note: Chemistry purists will argue there is only one "real" hardness number (the GH value). They are correct in this assertion, but we'll yield to the now-common ponding practice of lumping both the Carbonate (KH) and General (GH) readings under the combined heading of "Hardness". While the purists are technically correct, this nomenclature goes against the grain of "popular knowledge". For this reason, we've elected to go with the flow. If you are a purist, take a deep breath and mentally substitute "Alkalinity" for "Carbonate Hardness"

The subject of water "hardness" gets complicated by being split into two completely unrelated values. There is a General Hardness value (also called "Permanent Hardness", "Calcium Hardness", or "True Hardness") and a Carbonate Hardness value (properly called "Total Alkalinity", but also called "Temporary Hardness", "Potassium Hardness" (bleech!), or more generally as your "buffering capacity"). When you purchase your pond water test kits, make sure you get one which reads each value. Both numbers are important and each requires a separate test.

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Carbonate Hardness (KH)

Carbonate Hardness (KH)
The single most important hardness number is Carbonate Hardness or "KH". Not surprisingly, this is also the most variable measurement. As natural acids are released into the water during nitrification, it is the carbonate hardness which is responsible for neutralizing them. You can think of your carbonate hardness number as being a chemical sponge for acid. When the KH level is correct, the ponds pH remains fairly constant. When the KH drops, the pH crashes toward the acid end of the scale killing plants, fish and biofilter. For this reason the Carbonate Hardness test is of critical importance in heavily stocked koi ponds. Fortunately, a moderately high KH tends to occur naturally in most groundwater sources due largely to the presence of calcium carbonate, sodium carbonate and trace amounts of sodium bicarbonate. The KH value reflects quantitatively how much carbonate is present in a water sample and therefore is directly indicative of the waters buffering capacity.

Acceptable Carbonate Hardness Limits
The range of 80 mg/L to 120 mg/L (4.5 to 6.7 DH) is generally specified as being acceptable for koi and goldfish. If less than 80 mg/L of dissolved carbonates are present, pH swings can become problematic and the fish may become stressed. If the KH value drops below approximately 60 mg/L, biofilter operation may become unstable. By about 50 mg/L widespread death of fish from acidosis, pH shock and osmotic distress can be expected. Carbonate values greater than 120 mg/L are not particularly harmful to koi but are ideally avoided due to the associated higher pH and the corresponding increase in ammonia toxicity. A measurement of 105 mg/L (5.9 DH) is considered ideal for koi and is worth striving for.

The Phenomena of Buffering
So why are we so concerned with carbonates? Carbonates in solution exhibit a phenomena known as "buffering". If an acid is introduced to a water sample containing carbonates, the carbonates will react strongly with the acid and neutralize it, releasing carbon dioxide gas and a small amount of heat. It is interesting to note that even though carbonates are consumed, the overall pH of the water sample changes far less than you would expect. This effect is called "buffering" and is due to a quirk of chemistry involving the exchange of hydroxl ions and re-bonding. Simply put, carbonates stabilize the pH as long as they are present in sufficient amounts. When the carbonates become depleted, the pond is in grave danger because the input of even a small amount of acid will cause a large pH swing killing fish, plants, and your biofilter.
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Raising Carbonate Hardness (KH)

Increasing The Carbonate Hardness (KH)
Increasing a ponds carbonate hardness is fairly trivial. We can simply add a soluble carbonate-containing compound to the pond and a corresponding increase in carbonate hardness will result. The best tool for this job is sodium bicarbonate (i.e. "Arm & Hammer" baking soda). Sodium bicarbonate is non-toxic to fish, cheap, concentrated, and universally available and dissolves quickly in water. It is not dangerous to store and does not require special precautions during handling. With the single exception of increasing the ponds overall pH, sodium bicarbonate does not affect any other water parameter. It will not harm your plants and has no negative effects on the biofilter.

Sodium bicarbonate ("baking soda") is quite basic and will quickly raise the pH of the pond to 8.4. Because ammonia becomes rapidly toxic at increasing pH levels, even so-called "trace" amounts can cause serious harm to fish. If you need to make a large carbonate hardness change, do so over a period of several days unless your carbonate level has "crashed" (KH less than 50 ppm). Failing such an emergency, it is recommended that a maximum rate of change be limited to 20 mg/L per 24 hour period to avoid pH stress, and osmotic shock. Prior to making a hardness change it is recommended that an ammonia test be conducted to verify that no ammonia is detectable.

Increase KH: The Formula
As long as the pond is not currently suffering from a pH crash, (please click here to learn why a crash upsets our mathematical applecart), it is a simple matter to calculate the amount of raw carbonates needed to produce a given increase in KH hardness. The general formula is:
change in mg/L * pond volume (L) = mg of carbonate
Lets assume we want to obtain a "perfect" carbonate hardness value of 100 mg/L in a pond containing 500 US gallons. This pond currently has a measured KH value of 60 mg/L. Proceed as follows:

Step 1: Convert US gallons to liters.
(Note: There are 3.785 liters per US gallon).
Volume in US gallons * liters per gallon = volume in liters
500 gallons * 3.785 = 1892 liters
Answer: 500 US gallons equals 1892 liters
Step 2: Calculate how many mg/L we must add to achieve our target carbonate hardness number.
Target Hardness - Current Hardness = Amount Of Change
100 mg/L - 60 mg/L = 40 mg/L.
Answer: Change needs to be 40 mg/L of carbonate.
Step 3: Multiply the pond volume (in liters) by the "Amount Of Change" from above.
Pond Volume * Amt Of Change = mg of carbonate to add
1892 liters * 40 mg/L = 75,700 mg (75.7 grams)
Answer: We need to add 75.7 grams of carbonate
We now know how many grams of carbonate we need to add... but we need to translate this number into something meaningful. Could we simply add this amount of baking soda? NO. The reason stems from the fact that baking soda isn't a "pure carbonate". In fact, nothing is. Carbonate-containing compounds also contain other elements which do nothing whatever to help our buffering.

If you have no desire to dig deeper into the inner chemistry of this subject, go ahead and skip over this next bit. You'll find we've done the math for you on several common carbonate- containing compounds and summarized things neatly in a table at the end of this section.

Carbonates occur in many compounds but are always tied to other elements. Examples are sodium bicarbonate, sodium carbonate, calcium carbonate, etc. As we've mentioned, a good source of carbonates is household Baking Soda, known to chemists as Sodium Bicarbonate. Sodium bicarb has the chemical formula NaHCO3. If we take a close look at this compounds molecular structure, we see that each molecule is actually composed of the following quantities of elements:
• 1 atom of Sodium (Na)
• 1 atom of Hydrogen (H)
• 1 atom of Carbon (C)
• 3 atoms of Oxygen (O3)
By careful study of this breakdown we can see that not all the atoms in sodium bicarbonate will contribute to our buffering. Buffering is done entirely by the Carbon and Oxygen atoms when they combine to form a carbonate. Some elements, (like Sodium & Hydrogen in this example), are simply along for the ride. How then do we determine the actual percentage of the carbonate component? If you have a Periodic Table Of The Elements
handy, it’s pretty simple.

Periodic Table Of The Elements

The following table lists the first 36 of the known 109 elements in the Periodic Table Of The Elements. The table below is sorted according to each elements order in the Table, i.e., lightest through heaviest. Elements heavier than Krypton have been omitted as they are of very little concern to ponders.
# Element Symbol Atomic Wt
1 Hydrogen H 1.01
2 Helium He 4.00
3 Lithium Li 6.94
4 Beryllium Be 9.01
5 Boron B 10.81
6 Carbon C 12.01
7 Nitrogen N 14.01
8 Oxygen O 16.00
9 Fluorine F 19.00
10 Neon Ne 20.18
11 Sodium Na 22.99
12 Magnesium Mg 24.31
13 Aluminum Al 26.98
14 Silicon Si 28.09
15 Phosphorus P 30.97
16 Sulfur S 32.06
17 Chlorine Cl 35.45
18 Argon Ar 39.95
19 Potassium K 39.10
20 Calcium Ca 40.08
21 Scandium Sc 44.96
22 Titanium Ti 47.90
23 Vanadium V 50.94
24 Chromium Cr 52.00
25 Manganese Mn 54.94
26 Iron Fe 55.85
27 Cobalt Co 58.93
28 Nickel Ni 58.71
29 Copper Cu 63.55
30 Zinc Zn 65.38
31 Gallium Ga 69.72
32 Germanium Ge 72.59
33 Arsenic As 74.92
34 Selenium Se 78.96
35 Bromine Br 79.90
36 Krypton Kr 83.80

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The first step is to calculate the relative amount of each element in the compound using the atomic weight of each atom, as follows:
Element Atomic Wt # atoms Total Atomic Wt
Sodium 22.99 1 atom 22.99
Hydrogen 1.01 1 atom 1.01
Carbon 12.01 1 atom 12.01
Oxygen 16.00 3 atoms 48.00

Total Weight Of Compound: 84.01
Once we know the atomic weight of each element, we can add them all together to get the total atom weight of the compound, in this case 84.01. This is properly called the "Formula Weight" and represents the combined atomic weights of all the compounds constituent elements.

Now we need to add-up only the carbonate (carbon and oxygen) totals, as follows:
Element Atomic Wt # atoms Total Atomic Wt
Carbon 12.01 1 atom 12.01
Oxygen 16.00 3 atoms 48.00

Total Weight of Carbonates: 60.01
For sodium bicarbonate, we now know that on a weight basis, 60.01 parts out of 84.01 parts contain carbonates. Let’s convert this to a percentage for easier handling as follows:
carbonate total * 100 / formula weight = % carbonates
60.01 * 100 / 84.01 = 71.432%
Answer: 71.432% of NaHCO3 by weight is carbonate.
Having calculated that common baking soda is about 71% carbonates, we can now convert our raw carbonate grams into actual grams of sodium bicarbonate, as follows:
grams of carbonate / (available carbonate / 100)
75.7 / (71 / 100)
75.7 / 0.71 = 106.619 grams.
Answer: 106.619g of NaHCO3 yields 75.7g of carbonates.
Now you can see why we needed to convert our "raw carbonate" number into an equivalent grams of sodium bicarbonate. If we had simply added baking soda using the "raw carbonate" number (75.7 grams) we would have fallen short of our target by about 29%. It’s unlikely this much of an error would have been fatal to our fish, but we would have been scratching our heads a bit when the calculated carbonate dosage didn't produce the expected rise in KH.

This same process can be used with other carbonate-containing compounds to convert raw carbonate requirements into a more meaningful material weight. If you are a maschochistic nerd (like me!) you might want to try this manipulation on the following compounds and compare your results to the table a bit later on.
• Sodium Carbonate (Na2CO3)
• Calcium Carbonate (CaCO3)
• Potassium Bicarbonate (KHCO3)
• Potassium Carbonate (K2CO3)

For The Chemically-Challenged, Recess Is Over
Okay... that last part was pretty ugly. If I lost you in the middle of the chemical Babylon, I apologize profusely. As promised, here is the whole shebang in a pre-digested form for my non-nerd friends:

Chart #1: Carbonate conversion factors for a number of common "fish-safe" compounds:
Compound Name Formula F.W CO3 w CO3 %
Sodium Bicarbonate NaHCO3 84.01 60.01 71.432%
Sodium Carbonate Na2CO3 105.99 60.01 56.618%
Calcium Carbonate CaCO3 100.09 60.01 59.956%
Potassium Bicarbonate KHCO3 100.12 60.01 59.938%
Potassium Carbonate K2CO3 138.21 60.01 43.419%
Chart #2: Required amount of various compounds required to alter 100 gallons (378.5 liters) of water a specified amount.

Amount NaHCO3 Na2CO3 CaCO3 KHCO3 K2CO3
5 mg/L 2.649g 3.342g 3.156g 3.157g 4.359g
10 mg/L 5.298g 6.684g 6.312g 6.314g 8.718g
20 mg/L 10.596g 13.368g 12.624g 12.628g 17.436g

Extra Credit:
Getting back to our problem of adding baking soda to increase our hardness. We've calculated we need to add a total of 40 mg/L of carbonates to our pond. Over how many days should we spread this change to avoid pH and osmotic shock problems? (Keep in mind that our "Safe Rate Of Change" is 20 mg/L per day).
Amount To Change / Change Per Day = Days
40 mg/L / 20 mg/L per day = 2 days
Answer: Make the change over a period of 2 days.
Note: In the event you are treating a pond whose carbonate buffers are severely depleted (i.e., less than 50 mg/L) it may be prudent to exceed the stated "Safe Rate Of Change" above. If the pH is found to vary wildly from morning to afternoon, cease feeding immediately and adjust the hardness to attain 70 mg/L as soon as possible. Monitor the ammonia level carefully. If ammonia is detected at any time, immediately dose the pond with AmQuel (or equivalent) at the recommended label rate and increase aeration. When carbonate hardness reaches 70 mg/L resume carbonate dosing at the recommended 20 mg/L per day limit until the desired hardness has been reached. It is interesting to note that rapid changes toward the basic end of the pH scale are much less stressful to fish than those toward the acid end.

A Word Of Caution About Carbonate Affecting CO2 Levels
Adding any carbonate-containing compound to pond water results in the liberation of carbon dioxide (CO2) gas. Carbon dioxide is a colorless, odorless and tasteless gas which can block the oxygen-exchange mechanism in fish. The amount of carbon dioxide liberated is a direct function of the ponds initial pH, the temperature of the water, and the amount of carbonate being added. When large amounts of carbonates are suddenly added to a pond with a very low pH, excess carbon dioxide may be released resulting in oxygen starvation. Note that dissolved oxygen test kits may still show oxygen levels at or near saturation, even though fish are gasping at the surface for air. This condition is similar to nitrite poisoning in that the fishes ability to absorb oxygen which has become impaired... not the ability of the water to actually carry oxygen. Fortunately, this condition is seldom seen in practice. This condition is not readily reversible by the application of hydrogen peroxide or other oxygen-enhancing substances. Generally, the only course of action is fierce aeration which causes rapid mixing of the water and subsequent out gassing of the carbon dioxide burden to the atmosphere. Floating plants in full sunlight can be of some assistance in removing this surplus CO2, but their effects are slow by comparison.

Converting Between Measurement Systems
We've seen that both the DH and mg/L systems are used to measure hardness. How do we convert from one measurement system to another? Like this:

To convert from DH to mg/L, multiply the DH number times 17.9:
Example: Convert 6 DH to equivalent mg/L.
DH * 17.9 = mg/L
6 * 17.9 = 107.4 mg/L
Answer: 6 DH equals 107.4 mg/L
To convert from mg/L to DH, divide the mg/L by 17.9:
Example: Convert 107.4 mg/L to equivalent DH.
mg/L / 17.9 = DH
107.4 / 17.9 = 6 DH.
Answer: 107.4 mg/L = 6 DH
Note: mg/L and ppm are interchangeable units, i.e. 100 mg/L = 100 ppm.

Ponding Trivia:
You may be wondering how "KH" became the shorthand abbreviation for Carbonate Hardness when "CH" would seem to be the logical choice. It turns out the "KH" designation is an artifact of German origin. Years ago a mixture of sodium bicarbonate and sodium carbonate known as "Kalkwasser" (chalk water) was used to correct carbonate-deficient water. Chemists noted this "Kalkwasser" affected primarily the carbonate hardness number so the measurement of that hardness was referred to as the "Kalkwasser Hardness" or "KH" for short. The term stuck. Of course, the fact that many of the test kit manufacturers are based in Germany helps as well.

The Case Of The Disappearing Carbonates
So we've now learned to measure and modify our dissolved carbonate level. The next question is "What happens to our carbonate hardness level? Why does it drop? How fast is it consumed and by what?" Answers follow below.

The Effect Of Ammonia On Carbonate Hardness
We know that ammonia is produced by fish and aquatic animals through their gills, feces and urine. We also know that certain bacteria (nitrosomonas) utilize this ammonia via the Nitrogen Cycle and use it for food. What you might not realize is that the biofilter bacteria directly consume carbonates at a fairly high rate of speed. Biofilters consume carbonates both directly via bacterial action and indirectly by the production of nitrous acid. How exactly is this?

Consumption Of Carbonates By Bacterial Action
An established biofilter is capable of turning ammonia into nitrite and nitrite into nitrate. The bacteria responsible for this change are Nitrosomonas and Nitrobacter. Together, they consume about 7.2 mg of carbonates for every 1 mg of ammonia. When you consider that 1 kg of koi food containing 38% to 40% protein will produce an average of 40 grams of pure ammonia, this means that 295.2 grams (295,200 mg) of carbonates will be consumed.

Think about that statement for a second. One kilogram (1000 grams or 2.2 lbs) of food produces about 40 grams of pure ammonia which takes 295,200 mg's of carbonates to convert to nitrite! Them's sum big gophers, Vern! Just for grins and giggles, let’s see how many milligrams of carbonate are available in our 500 gallon (1892 liter) pond. The general formula is:
mg/L of carbonates * volume in liters = total mg's of carbonate.
Let’s assume we have already added sufficient baking soda to get our ponds carbonate hardness up to an optimal 100 mg/L. How many total milligrams of carbonate do we have available?
100 mg/L * 1892 liters = 189,200 mg/L (189.2 grams)
Answer: 189,200 mg/L (189.2 grams) of carbonate
A bit of quick math will show us that, even if we could actually let the ponds carbonate reserves fall to zero, we would still be short 106,000 mg's (106 grams) of carbonate! (295,200 mgs required - 189,200 mg available = 106,000 mgs short). In reality we need to keep our carbonate level at or above 80 mg/L if we want happy fish. Assuming we started at 100 mg/L and decided we would never let the KH drop below 80 mg/L we'd need to add 257,360 mgs or 257.36 grams (295,200 - 37840 = 257,360 mg's) divided into small amounts on a daily basis just to stay within the acceptable range. This translates into 9 ounces of baking soda.

As you can see, the biofilter consumes carbonates at a remarkable pace.

Let’s take our example even further. Let’s say we have 20 lbs of healthy koi swimming around in our 500 gallon pond. Because we love and cherish our fishy friends, we are going to feed them at the hatchery-recommended "growth rate" of 4% of their body weight per day. Let’s calculate how many milligrams of carbonate will be consumed on a daily basis.

Step #1: Compute the weight of our daily feed ration
weight of fish (lbs) * 4% = daily feed ration (lbs)
20 lbs * 0.04 = 0.8 lbs per day
Answer: 0.8 lbs of food per day
Step #2: Convert lbs/day into grams/day (Note: 1 lbs = 454 grams)
daily ration (lbs) * 454 = daily feed ration (grams)
0.8 lbs * 454 grams = 363 grams food per day
Answer: 0.8 lbs = 363 grams
Step #3: Compute ammonia produced (each gram of food produces 0.04g pure ammonia)
grams per day * 0.04 = grams ammonia produced per day
363 grams * 0.04 = 14.52 grams of ammonia per day
Answer: 363 grams food = 14.52 grams ammonia
Step #4: Compute carbonate consumed. (each mg of ammonia consumes 7.14 mg of carbonate)
grams of ammonia * 7.14 = grams of carbonate consumed
14.52 grams * 7.14 grams = 103.67 grams of carbonate
Answer: 103.67 grams of carbonate would be consumed
Chart #3: Converting Grams to Kitchen Measure for Sodium Bicarbonate
1/4 tsp=1.25g 1/2 tsp=2.5g 3/4 tsp=3.75g 1 tsp=5.0g
1/4 tbsp=3.75g 1/2 tbsp=7.5g 3/4 tbsp=11.25g 1 tbsp=15g
1/4 cup=59g 1/2 cup=118g 3/4 cup=177g 1 cup=236g
1 pint=473g 1 quart=946g 1 gal=3785g 5 gals=18,925g

Copyright © 1998 by Roark. All Rights Reserved.
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Page rev 7.12 of 06FEB98

Lowering Carbonate Hardness (KH)

Decreasing the Carbonate Hardness
Decreasing the carbonate hardness of a pond can be accomplished in one of three ways:
• Increasing the natural biological load
• Dilution of carbonate level by rain, distilled/deionized water, or other low-carbonate water
• Manual addition of acid
Note: You may notice that commercial water softening "filters" and aquatic "pillows" of polystyrene resin beads are not found on this list. These technologies do absolutely nothing to reduce the KH. These methods are known collectively as "ion-exchange water softening" and affect only the General Hardness (GH) number. Carbonate hardness (KH) remains totally unaffected... a fact which continues to remain undocumented on the product labels themselves.

KH Reduction Method #1: Increase The Natural Biological Load
If you need to burn-off a small amount of carbonates and are preferential to the "green" approach, you can elect to do nothing more than feed your fish and wait. The resultant ammonia produced by the fish is converted by the biofilter into nitrites and nitrate. This conversion consumes carbonates and will naturally reduce the KH level. How much reduction is possible? Depending on your stocking level, quite a bit. As a point of reference, for the biofilter to process 1 gram of ammonia requires the consumption of 7 grams of carbonate. As a further point, one pound of koi food will result in the production of 40 grams of ammonia. Do the math. (We'll cover this ad nauseum a bit later, but just for fun do the numbers now. Too lazy to figure it out? No problem. Each pound of food consumed will require 280 grams of carbonates!)

KH Reduction Method #2: Dilution
Water which is only slightly carbonate-heavy (125 ppm to 140 ppm) can be often be softened by dilution with deionized water or rainwater. For small ponds diluting the KH is a fast, safe way to reduce carbonate levels if a convenient rainstorm appears. For smaller ponds, distilled water or a low-carbonate water source may be used. If your water contains a large amount of carbonates however, use of the acid-reduction method is indicated.

KH Reduction Method #3: Use Of Acid
The addition of nearly any strong acid to your pond will result in the rapid consumption of carbonates, thereby reducing the KH. Acids preferentially attack the KH value while leaving the GH value intact. While virtually any acid will work, hydrochloric acid is the most suitable and the safest from a chemical standpoint for fish and plants. If you are considering this method, please read and understand the section on Acid Safety first.

Hydrochloric Acid
Also known as "pool acid", "muriatic acid" or by its technical name, "hydrogen chloride", hydrochloric acid (symbol HCl) is a simple two-element acid consisting of a single hydrogen atom bonded to a single chlorine atom. This is an exceptionally strong, stable acid whose byproducts are largely non-toxic to fish and plants. Five strengths are commonly available, as follows:
• 8.7% solution . Called "spa-strength pool acid", this is a rather dilute HCl designed for use in spas, hot tubs and other small bodies of water. This strength is ideal for making controlled adjustments in ponds in the sub-2500 gallon category. It can be obtained from your local pool supply or hardware store in 16 and 32 ounce containers. It is quite cheap. Locally I obtain this for about $5 for a 16 oz bottle.... which easily lasts a year or more.
• 22% solution . Called "consumer-strength pool acid", this is designed for use in home swimming pools or large spas. It is much more concentrated than "spa-strength" acid and should be used only in 2500 gallon and larger ponds. It is typically available in 1 and 5 gallon containers at your local pool supply or hardware store. A little goes a long way. Depending on your source, it can actually be cheaper than the weaker "spa grade" acid. I've seen gallon containers sold for under $4 locally. In some locations, this is the strongest "pool acid" you can find over-the-counter.
• 31.4% solution. Called "full-strength pool acid", this is designed for use in very large swimming pools or commercial water treatment operations. It is much more concentrated than "spa-strength" or "consumer- strength" varieties. Consider using this only if your pond is 10,000 gallons or larger. It is available in 1 and 5 gallon containers at your local pool supply store. Depending on your local regulations, you may find this strength at the hardware store. Depending on your source, it can actually be much cheaper than the weaker "spa grade" or "consumer grade" acids.
• 30% solution. Available only through scientific supply houses, as "technical-strength HCl". This highly concentrated acid is quite pure, very potent, and absolutely free from any chemical additives (except water) which might harm your fish or plants. Quantities as small as 4 ounces are available. If you have very limited storage space and are not afraid of accurately measuring small amounts, this strength may be successfully employed if extreme caution is employed. For the casual ponder however, this is overkill and difficult to handle. It is also comparatively expensive.
• 37% solution. Called "reagent-strength HCl", this acid is designed for use where ultra-pure, ultra-strong; analytical-grade HCL is required. It can be used in very large ponds or aquaculture tanks where purity is of paramount concern. It is far too potent to be used by the casual hobbyist. This stuff is pure, concentrated evil if it gets on you, your clothes, etc. The additional expense and shipping precautions are generally not worth the hassle. Mixing liberates lots of heat. Expensive stuff, too. Plan on paying between 50 cents and a dollar per ounce.

Pro's & Con's Between HCl Grades
Because the 8.7% and 22% "pool grade" acids are cheap and plentiful, many people will elect to use them. While there is no conclusive, documented proof that the pool grades contain anything but pure hydrochloric acid and water, there are rumored to be instances where acid manufacturers have added other wetting and dispersal agents which have harmed fish. Personally, I'd chalk this up to a case of accidental misuse by the ponder. I've used the 8.7% grade manufactured by SpaKem hundreds of times and have had no problems.

Which Grade?
If you are raising some particularly expensive fish and don't want any surprise additives, purchase the mail-order only "technical grade" and dilute it with distilled water to a more manageable 8.7%. This high-purity acid is required to meet strict manufacturing quality standards and is routinely used as a raw material in laboratories and refineries. I would not recommend use of the "reagent grade" variety under any circumstances. At 37%, this stuff is just way too nasty for amateur chemists to handle safely.

Decrease KH: The Formula
It is a simple matter to calculate the amount of 8.7% HCl needed to produce a given decrease in KH hardness. The general formula is: measured KH in mg/L - desired KH in mg/L = mg/L of KH to be removed Once we know how many mg/L we need to remove, we can use the KH Acid Reduction Table to calculate the amount of acided needed. Example: Let’s assume we want to obtain a "perfect" carbonate hardness value of 100 mg/L in a pond containing 500 US gallons. This pond currently has a measured carbonate hardness value of 115 mg/L. Proceed as follows: Step 1: Calculate mg/L of reduction needed measured KH in mg/L - desired KH in mg/L = mg/L of KH to remove 115 mg/L - 100 mg/L = 15 mg/L Answer: We need to drop our KH by 15 mg/L to obtain our target of 100 mg/L Step 2: Use the table below to calculate our acid dose a). On the left margin, find the ponds displacement in liters. (Use the 500 gal scale) b). Move across this row until you find the column titled "15 mg/L". Answer: You will need to add 35.48 ml (about 1.2 fluid ounces) of acid to drop 500 gals by 15 mg/L. To selectively reduce the carbonate level of a pond, use the table below: Table #1: mL of 8.7% Hydrochloric Acid Required For Various mg/L Carbonate Reductions

Carbonate Reduction in mg/L

Gal Liter 5ppm 10ppm 15ppm 20ppm 25ppm 30ppm
100 379 2.37 4.73 7.10 9.46 11.83 14.90
200 757 4.73 9.46 14.90 18.92 23.66 28.39
300 1136 7.10 14.19 21.29 28.39 35.48 42.58
400 1514 9.46 18.92 28.39 37.85 47.31 56.78
500 1893 11.83 23.66 35.48 47.31 59.14 70.97
600 2271 14.19 28.39 42.58 56.78 70.97 85.16
700 2650 16.56 33.12 49.68 66.24 82.80 99.36
800 3028 18.92 37.85 56.78 75.70 94.63 113.55
900 3407 21.29 42.58 63.87 85.16 106.45 127.74
Rule of Thumb
10 mL of 8.7% HCl acid will reduce 425 gallons of water by 5 ppm.

Note: For larger or smaller ponds, you can scale the table proportionately. i.e., for a 50,000 gallon pond, use the "500 gallon" scale and multiply the result by 100.

Important: This table above is only valid for solutions of 8.7% HCl (also known commercially as "spa grade muriatic acid"). Be sure to check the label. Do not use this chart with "pool strength" acid as this solution is much stronger!

Calculating A Safe Acid Dose
At first blush, our example above would seem to indicate you could simply toss 78 mL of acid into your pond and walk away whistling. Wrong answer, Buckwheat! Adding acid causes the pH to drop sharply before the buffering effect catches up. This sudden drop can and will kill fish. Acid additions designed to drop the KH more than 5 mg/L need to be broken-up into smaller doses and applied over a period of time. Some rules of thumb designed to keep you out of trouble:
• Safe: Drop 5 mg/L of carbonate hardness every 12 - 24 hours.
• Safe: Drop 0.1 pH units every 3 hours for up to 12 hours
• Safe: Drop 0.2 pH units once every 24 hours.
Note: These rules of thumb assume the ponds hardness is above 80 ppm. These guidelines tend to fall completely apart when the hardness drops below 80 ppm or there are other stressors present (i.e., ammonia, nitrites, disease, high temperatures, low oxygen. etc). When in doubt, add 25% of the recommended dose, turn your pump and spraybars on full and wait 30 minutes. Remeasure your pH. In an emergency, excess pool acid can be quickly neutralized by adding unscented household baking soda. See the section on Raising Carbonate Hardness (KH) for full details.

Copyright © 1998 by Roark. All Rights Reserved.
Email comments to: roark7@aol.com
Page rev 7.12 of 06FEB98

08-17-2007, 04:55 AM
Waddya do in a flow through ( open ) at a hardness of five-8 and the source dries up ?
700,000 Egal. Empiracle as oppsed to Imperial...:cheer:

08-17-2007, 11:25 AM
Waddya do in a flow through ( open ) at a hardness of five-8 and the source dries up ?
700,000 Egal. Empiracle as oppsed to Imperial...:cheer:

Please tell:punk1: :clap:

08-17-2007, 11:50 AM
My only question is why would you lower your carbonate hardness? Is that not just like playing with fire?

08-17-2007, 02:51 PM
It can go too high. Leaching!!! Too much of a good thing and all...

i'm nut's
08-19-2007, 06:30 PM
It can go too high. Leaching!!! Too much of a good thing and all...

Yeah, like me..............:cool3:

05-06-2008, 11:39 PM
Thanks for the usefull info, I,m about to dig a couple of mud ponds and I tested the ajacent spring fed creek which will form part of the water source for the ponds (expect some seepage as ground is usually boggy) and got a reading of 7.0 for PH but no reading for KH or GH (no color change at all!). Obviously I have no fish to worry about at this stage, so what is the best, and how much, chemical should I add to get a acceptable KH. Got very low readings for nitrites etc.
Thanks again.