Backyard Aquaponics
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Help! My yellow perch are dying. I think from high nitrates. Around 160ppm. I have harvested fish, added plants, added red worms and replaced water. I have stopped feeding and still after 2 weeks, the Nitrates have not come down and the fish (year old) are still dying. I have a 300 gallon fish tank for my flood and drain system and 9 grow beds around 18 gallons each. The system is 3 years old and the tomatoes and peppers are huge and every plant seems to be thriving. I am down to 7 adult fish but some of them are not looking too good. ANY SUGGESTIONS?

Are yellow Perch particularly sensitive to nitrates?
When you say "around 160ppm" is that just due to that being the maximum reading in the API test kit? If so, I'd suggest diluting your 5ml sample with 15ml of pure water, and re-test with 5ml of that mix, and report back on the result. Dont forget to multiply the result by 4 to give nitrates in the FT water sample.

I've had nitrates up around 500ppm for many months with Rainbow Trout, with no apparent ill effects, due to not enough large plants in the system for the number of fish. Now the plants are larger, and after a few months of reduced feeding, nitrates are back to around 100ppm and gradually decreasing, so I have upped the feeding again.

I use the API kit which isn't precise but based on the dark red color, the Nitrates seem to be hovering at the top reading 160ppm. I will retest as per your suggestion. These are my first perch so I am not sure if they are particularly sensitive.

I have had silver perch in a system with nitrates off the scale of my API kit and the fish were fine. Not sure if silver's are similar to yellows.

What the silver perch did not like was when the water temp got down to under 2 degrees celcius (35F). Once this happened I started to lose them. Whats your water temp like?

Just echoing comments above... my silver perch and jade perch and eel tailed catfish don't seem at all worried about having spent most of their lives in nitrates well over 300. They taste good and grow as fast as expected. Your yellow perch in USA are unlikely to be closely related to Australian native perch but they'd have to be extremely sensitive if it's the nitrates that are killing them.

Assuming standard water parameters are testing normally, are you confident that nothing toxic has got in to your system?

The water I add to the system is from a well high in the Rocky Mountains. It has been tested & is very pure but I will run some tests on it anyway. Water temp has stayed a constant 60 degrees F. Ph consistently 6.8, ammonia 0, nitrites 06

Sounds like the sort of pristine water most of us would love to have access to.

I was wondering about something like a neighbour spraying something on their garden. But it sounds like you might not be in an urban setting.

Don't know where I got the info but I have some notes saying nitrites above 0.5 can irritate/distress fish - but that they shouldn't be lethal till about 10 times that level.

in regards to lowering the nitrates... I feel your pain. Have been trying to do it for a long time. Have doubled plants and had quite a few fish dinners. Also tried lowering feeding. It has made a difference but I don't think I can really get them down until I savagely correct my ongoing overstocking. When nitrates do fall from such high levels (eg 400), they take a long time to do so... days to weeks.

I'm afraid I'm not being very helpful to you.

Thanks for all the comments/info. I am in a rural mountain setting at 9200 feet elevation and the system is indoors. Had about 30 fish a few months ago and from mortality/harvesting maybe 5 or 7 are left. Hoping they make it!

You say you are using API test kits and that your Nitrite reading is 06???... This is a little confusing... I'm assuming you meant either 0.6 or 6.0ppm

The API kit doesn't have an individual colour reading on the chart for 0.6, it goes 0.25, 0.5 then jumps up to 1.0... and I very much doubt anyone could discern between 0.5 and 0.6 with the naked eye.

Plus, the chart tops out at 5.0ppm.

I would redo your Nitrite test as per the instructions provided with the test re pre-shaking, amount of drops, standing time before reading etc.

At 1.0ppm Nitrite can start to affect fish health and your water should be salted with plain sea salt (ie: plain pool salt with no anti-stain agents etc) to a level of 1gm per litre of water, to mitigate the harmful effects of the Nitrites.

At 2.0ppm the Nitrite will definitely start having an effect on fish health and you should be doing regular 30% water changes to reduce it until it begins dropping on it's own. Ensure you salt any top-up water to 1gm per litre so that you aren't diluting the 1gm/Ltr rate in the main system.

The nitrites are 0. That was a type o.