Sort of, New Pond Troubles - Sick fish

[StoreyWilson]

Lets get through the uncomfortable introductions. I am a new koi keeper. I built a 600 gallon, in ground, concrete bock with fiberglass liner pond. About 1/3 of the total water volume is mechanical and biological filtration. The pond has been active for 5 months. The pond has cycled to a nice stable clear.

I have a huge amount to learn.

undetectable NO2
undetectable NO3
PH 7.5-8.0
KH 80-120
GH 120-150
salt 0.3% roughly.

I added 5 new 3-4 inch koi approximately 60 days ago.

I was not paying close enough attention to the progression of what turned out to be a very sick fish. My diagnosis was, Aeromonas Hemorrhagic Septicemia. In my ignorance I thought that the koi fish was changing color as it was growing. However looking back, the red coloration was a bacterial infection taking over the the fish. The rear fin and then body were heavily infiltrated with red vascularization. I was simply not looking closely enough each day. The fish was a bit distended and a few scales were beginning to pop out. I also noticed 2 pea sized blisters forming on the scales. The fish died very quickly after I noticed the symptoms. I think it all began and ended within 14 days time. This was 3 days ago.

I did a 25% water change immediately.

Today, I have another sick koi fish. lethargic behavior not eating. Slightly swollen eyes. Entire head of fish seems a bit swollen. The gill flaps seem swollen a bit. I think this is a scale-less variety koi. I isolated the koi. And this next observation is a strange one and I am embarrassed to admit, I never noticed. This newly sick koi is missing 3 of its fins entirely. No pectoral fins at all and only one ventral fin. And I mean completely missing. Nothing there not even a piece of fin.

The questions are:
1. Could these fish have come with this disorder or did they contracted it during the last 60 days?
2. Should I be water changing more frequently, every few days to get this bacteria out of my pond?
3. Does Melafix do anything really to the water quality or is this snake oil?
4. Are these even bacterial infections?

[RichToyBox]

Thanks for all the background information. The problems you describe are bacterial infections and would be best treated with Tricide Neo, which can be purchased on line.

You gave test results for everything but the ammonia. With nitrite and nitrate being undetectable, I wonder if your filters are even cycled yet. Ammonia burns the gills and skin which will allow for bacteria to enter the skin causing infections.

I hope the test results that you provided are from drop type test kits, and not dip strips which are very sensitive to age and often worse than unuseful as they can give erroneous readings.

The bad news is that your pond is really too small for koi. A general rule of thumb that I am familiar with is minimum of 1000 gallons, with a minimum of 250 gallons per koi. Koi grow to be large, many reach 30 inches, and need room to swim. Your pond is much better suited to goldfish, which need a minimum of about 25 gallons per fish. Some have been successful with small volumes but they are the exception, not the rule.

As for Melafix, it is very effective at removing money from pond owners pockets, but not often much more. There are better treatments which are designed for specific circumstances.

Bacteria are always present in all environments. You have large numbers living on and in you and they don't bother you unless you have a situation the lowers your immunity, and the same is true for the fish. Good water helps the fish to have a good strong immune system. If the bacteria get an opportunity to multiply and overtake a fish, it is time for antibiotic treatments, like with Tricide Neo.

With most ponds we recommend a minimum of 10% water change a week, but for small volumes the best bet is to monitor the nitrates and if they go up, then the water changes need to increase. Bacteria in the filters convert the ammonia to nitrite, and then the nitrite to nitrate, but there is no way to remove the nitrates except through water changes.

[StoreyWilson]

Thank you for the reply. I did forget the Ammonia measurements.

The ammoniameasurements were undetectable using a drop test kit.

The Ammonia, nitrate and nitrite have always been undetectable.

I will begin more frequent water changes and a Tricide Neo treatment.

I will find a good home for the extra koi fish, assuming that they survive.

[StoreyWilson]

Follow up:

None of the remaining fish have shown any signs of infection or stress behavior. The small pond is stable for now.

Thanks for the help.

[RichToyBox]

Great news. Always good to get reports back.

[DMon707]

I guess my pod is one of the exceptions. I've had 520 gallons concrete with a sand-filled wine barrel filter for 30 years. My five koi have grown fairly large ( up to 22') owing to the depth of the pond (raccoon proof depth). I've never had an ammonia problem except when housesitters overfeed. Feed sparingly and clean the filter regularly and you should be able to keep six koi in a six-hundred gallon pond.