Backyard Aquaponics
A place to discuss aquaponics

My system (3 half ibc gb, 1 ibc ft, splitflow)
Is in its 3rd year.

A month ago i put in 20 fingerling trout.its summer now and im still showing zero nitrates and i dont know why. Ive had good nitrates in the past but this years its been flat zero all the way. i only had a small walnut tree (now removed) and a couple of small tomatoes - i dont think enough plants to use it all up.

I can only think its because of algae?

My water is clear but i see some algae in the clay in patches. Could these patches be powerful enough to suck my nitrates?
How do i get rid of this algae?


I had no fish in the system for around 9 months through our english winter/spring.
The systems pump and water were all running during this time. I used to put in ammonia sometimes to test it and always had zero across nitra/ites and 0.5 ammonia.

Hey Moiz,

It looks a lot like moss to me. I'm not sure what the nutrient uptake from moss is like, but it usually grows in very moist places.

If it is moss, and you want to get rid of it, I'm not sure shade would do anything, since it usually grows in shady places. You might try picking it out by hand.

Does your system receive a lot of direct sunlight? Here, sunlight usually kills off moss, but encourages algae to grow.

What is the difference between the water line and the media surface?
If the water is high, you might be able to shorten the standpipe to drop the level a bit, and dry the moss out.

I'm not sure if the moss is causing your situation though. Tomato plants do have a high nutrient demand, and it could be possible that they are using up your nitrates as fast as they are produced.

Definitely need to drop the water level in the grow bed a bit. The media surface should not be damp - the light and moisture make it a good spot for moss to grow. Your veggies won't have any troubles going deeper for moisture so keep the surface dry once they are beyond the seedling stage.

If you're not having your plants turn yellow due to lack of nitrogen then the plants are still getting enough. It's not uncommon to run with a zero nitrate reading, the plants just use it as it is generated.

Another possibility is that denitrification is occuring somewhere in the system. If this is the case, it will be happening in the most stagnant zones where oxygen gets used up, and the giveaway will be the pH value. If your pH steadily declines then this wont be the case, but if your pH remains stable, then denitrification is probably occuring.

This is not a problem in terms of the health of the system (unless anaerobic zones grow uncontrolled), the only issue is loss of nitrate to the atmosphere where you'd prefer it to be used for plant growth.