What makes my nitrate readings high (0.5-1)

[Zaman]

Hello
I’m new to the forum and I appreciate your advice .
We’re located in Sinai, Egypt and unfortunately, no koi enthusiasts around..
we have 3 large natural ponds and one small hydroponics koi pond . All use RO water , oldest pond has 20 years , never had any problems with water quality or fish ( occasionally we lost fish to predator birds or cats over the years ) .
Hydroponics pond , 2 years old, 850 liters, around 50 young koi and butterflies there at the moment (10-20cm, 1 to 2 years old ) . It works as an inverted fountain with plant buckets all around and water falling back to pond creating waterfalls , daily we add 5-10% water due to evaporation and plants, in summer twice a day . Recently we moved 15 butterflies out to bigger natural pond, they were growing much faster than others ..
afterwards, About 2 weeks ago , 1 koi died at night , in morning pond was smelly , ammonia .25 , nitrate 1
Changed 50% water , ammonia back to 0, but nitrate 0.5
Since than we’ve changed 30 % water every few days ( besides daily adding water ), but nitrate always at best 0.5
We use API kit , 7.6 ph ( always, all ponds ) , nitrite 0 , high range ph 7.4-8
I’m wondering what is causing the high nitrate ?
What am I missing/ forgetting ?
Is it the fish growing and pooping more or water quality issue ( same water has perfect readings in other ponds ) .
Thank you
Lucy

[SimonW]

I am not expert, but I guess that you must give us the unit. As nitrate concentration of 1 ppm (the most commonly used unit here) is nothing. Nitrate is not good when it gets 50 ppm, deadly when reaches 200 ppm.

[Marilyn]

You mentioned a smelly pond and ammonia climbing. I suspect they spawned, hence the smell. What results is raised ammonia and subsequent higher nitrIte readings.

I think the confusion is you mentioned nitrAtes but I am unaware of any test that would measure nitrAtes with that much specificity. If I am mistaken, please let me know. Simon would be correct about the level of nitrAtes but since I believe we are actually dealing with elevated nitrItes, I would continue with water changes and a filter cleaning to remove as many of the eggs as possible.
Basically what happened with the spawning is that the filter became overwhelmed and the nitrIte reading is showing this. Bind the ammonia (if present), make sure to maintain adequate KH/alkalinity with baking soda so the filter can come fully back online.

[Zaman]

I made a mistake reading the results ..thank you for pointing that out
Nitrate moves between 5 -10 , it’s sometimes hard to tell which , it’s been going on two weeks now .
Since I now measure every day, I also noticed the ammonia of 0.25 few times . Mostly all tests come perfect except nitrate.
I have another issue I’d like to ask, I don’t think it’s related though, I will start another thread .

[RichToyBox]

I think that the main problem is overcrowding. Your 850 liters is about 225 gallons, and we recommend a minimum of 250 gallons for one koi, and you have around 50 fish. By our guidelines you would be allowed to have about 9 or 10 goldfish. The more crowded the pond, the less stable it is and the easier it is to have problems with the fish. The reason for the changing ammonia reading is most likely due to the amount of time after a feeding to the time of testing. The fish create more waste as they eat than at other times and overpower the filter system. As time goes on, the filter is able to catch up.

If it were me, I would remove at least half of the fish from this small tank and move them to larger ponds. It will improve the growth rates, improve the water quality, and improve the ability of the filter system.

[Zaman]

I totally agree , it sounds very reasonable , the pond is getting small as fish growing ..
I already moved 8 biggest fish (40 cm max ) about a month ago . There are still at least 10 others who I’d like to rehome . The plan was to leave only fingersize fish so they can peacefully grow on their own terms . There are that big size differences , same age ..
Plan didn’t work , something went wrong, those 8 are still here but all the original stock is unfortunately all gone -I started another thread about the big pond catastrophe.
Thank you

[trapper]

I made a mistake reading the results ..thank you for pointing that out
Nitrate moves between 5 -10 , it’s sometimes hard to tell which , it’s been going on two weeks now .
Since I now measure every day, I also noticed the ammonia of 0.25 few times . Mostly all tests come perfect except nitrate.
I have another issue I’d like to ask, I don’t think it’s related though, I will start another thread .

Don't worry yourself over the small amount of nitrate you are seeing as it won't bother your fish..