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Nitrate Levels High - Consequences of Prolonged Exposure for Fish

My AP system has been running successfully for the last month; however I can't get my nitrate level to lower.  Both of my 50 gallon GBs are full of healthy looking plants.  Why can I not get the nitrate level down?  Is prolonged exposure to nitrates bad for fish?  What signs will fish demonstrate if they are being affected by high nitrate levels?  Nitrate levels have been at about 160ppm for the last month.

I've attached a pic of my two 50 gallon GBs....last I have a 100 gallon FT.

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I should also note the fish seem to be doing great.  They're happy to eat and don't seem stressed.

160ppm should not be a problem for fish. I don't know about other species, but I recall tilapia being able to handle as much as 700ppm of nitrates. Sounds to me like you have some leeway before you have a problem, but I could be wrong.

Great picture, by the way. Everything looks pretty healthy! If your plants look healthy and your fish look healthy, then I don't think you should worry about your system. If you're concerned, just keep a close eye on things.

More Plants, a lot more.  I am in the same boat and the only way I have been able to drop Nitrate levels was but putting more, established plants in the grow bed.

Hi Roger,

A reading of 160ppm NO3 is not considered high in AP, but actually ideal for growing leafy plants. This amount of nitrates are not considered suitable for fruiting plants, although they do grow them. If you don't have a lot of growbed space and want to bring down the reading, go for a vine crop. In my experience, having bitter melon and cucumber plants etc in an AP system will quickly get you to low nitrates levels in a short time and they can be planted in a corner of the GB. The vine growing crops are a way to effectively increase GB size without the expense of added construction.

Check out this fact sheet, very helpful.  Notes 300-400 mg/L is low end of toxicity range for tilapia, mg/L is also equal to ppm.  Partial water change will help bring Nitrate down quickly.

Thank you for everyone's input!  Very useful information!

You're fine on nitrates. Actually in a pretty sweet range.  You just don't have enough uptake at the moment to bring down your levels.  At much higher levels, nitrates will start to interfere with your fishes' abilities to bind oxygen to hemoglobin, but you've got a long way to go before that happens.  In the meantime, the one negative effect can be aphid infestations and higher aphid reproductive rates.  Those suckers love high nitrates.  If you're having bug issues, dropping your nitrates can help get them under control, along with traditional control methods. . . 

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