Backyard Aquaponics
A place to discuss aquaponics

I've got an indoor drain and fill system that I've been trying to get in control the last few months:

* 20 gallon fish tank with ~12 two to three inch goldfish
* 40 gallon plant bed with herbs and flowers (for starters)
* 30 gallon sump tank
* I control the pH to about 7.0

I think I had the fish ahead of the plants for a while (Nitrate was > 150 ppm) and no plants would grow at all. I started doing water changes, got the Nitrate level down, and found that some plants would grow. Now the Nitrates are down to ~10 ppm and everything is growing well, but foliage is yellowish on many of the plants (see photo) - with the veins staying green on some.

Should I be adding or taking away fish or feeding more or less to target a certain Nitrate level? Any advice on the yellow foliage? I believe I have too much or too little of a nutrient, but not sure what.

Thanks! From Minnesota, USA

Most likely it's an iron deficiency. Are you adding any iron supplement?

No, I'm not adding iron. Can you recommend a product? Also, is nitrate level a useful metric to tell if I have enough fish poop compared to the plants I have going?

Maxicrop with added Iron will likely go a long way to solving your issue. Initially add 2x capfuls per 500L of water, then 1x capful per 500L of water, per week on an ongoing basis.

Nope!... Nitrate is a result of Ammonia conversion, the Ammonia in the system is primarily from fish urination and respiration, which happens even if fish aren't being fed or pooping, so Nitrate is constantly being produced in the system, while all the essential mineral nutrients that come from the fish poop could be deficient. This commonly occurs in systems with goldfish, koi, other ornamental fish etc, even if the fish are being fed, as their feed doesn't have sufficient levels of the mineral nutrients when compared to a quality commercial grade feed such as Skretting that is used for farmed edible fish.