Help with my high NITRATES needed...


Well-Known Member
Tortoise Club
5 Year Member
Platinum Tortoise Club
Jul 16, 2014
Location (City and/or State)
South Eastern Florida (U.S.A.)/Rock Hill S.C.
A few months ago, I set up two fish ponds out of pools.
They are about 1,400 gallons filled. And the rain has them FULL.
I have smallish 950gph pumps in each pond feeding spray bars that dump into home made gravity filters of my own design. They have been working fine. So fine that I'd gotten lazy about water testing aside from PH.
One side has a very, very large Jaguar cichlid. His water is just great. No Ammonia. No Nitrites and no Nitrates. I was thinking I'd have to upgrade to a higher flow pump. But so far, so good.
The other pond has 5 large Midas Cichlids in it.
Yesterday I found a dead Midas floating. He looked perfect. Obviously not killed in a fight.
I tested the water.
A trace of ammonia. (Almost none) the same trace of Nitrite. But a BIG bunch of NITRATE. Like over 30ppm.
I immediately dumped about half the water and placed a pillow sized sachet of activated carbon into the filter box for the stink and polution
..I was thinking NITRATE POISONING.
But, with no ammonia or Nitrite. How could I have such a high Nitrate level?
It puzzled me.
Now I'm guessing that the fish died for some other reason. He floated in there in the heat for maybe 48 hours (or more) and the dead fish was the sole cause of my high Nitrates.
Does that theory make sense?
I'm very curious.
I'll do another water test in 24 hours.


The Dog Trainer
10 Year Member!
Platinum Tortoise Club
Jan 9, 2010
Location (City and/or State)
Southern California
On an established system with adequate biological filtration, there should be no ammonia or nitrites. One dead fish in 1400 gallons shouldn't even register on your ammonia or nitrite test kit. 5 live ones in 1400 gallons is a very light load. Many people keep that many in a 100 gallon tank with no issue. I have four 10" fish and seven 8" fish, in a 130 gallon tank with a canister and back hanging filter, and no issues. One osphronemus, one Texas cichlid, one jack dempsy, one pleco, and 7 leporinus.

Nitrates present mean your biological filtration is working. Can't create nitrates if the two necessary bacteria aren't breaking down ammonia and nitrites. 30 ppm is no big deal and not toxic. Adding plants or increasing water changes will dissipate that number. Most freshwater fish can tolerate nitrate levels over 100ppm as long as it builds slowly and isn't instantly dropped to near zero with a huge water change. A big change in nitrate levels is worse than high nitrate levels. Your level is reasonably low at 30 ppm.

I think your COD was something else. Possibly fighting or some pathogen from the wild where you caught them.


Well-Known Member
5 Year Member
Platinum Tortoise Club
Jan 17, 2012
Location (City and/or State)
Sacramento, CA (Central Valley)
Agree with all Tom has said. 30ppm is actually low levels of nitrate. Water comes out of my tap with twice that level here! Nitrates is the end product of the nitrogen cycle so indicates the filter is working. But nitrates will build up in a closed system. So water changes or plants are about the only way to control. There are chemicals to absorb and remove nitrate, but that is prohibitive in a larger pond. Partial water changes are great if your source water is low in nitrates. Plants are a good way to keep nitrates lower as nitrates = plant food! Water hyacinth is an excellent plant for that and provides some shade cover for the pond as well. Koi will eat most plants but with your fish it should be a good option. HIgh nitrate will also therefore encourage algae growth.