A Question on Nitrogen Sources


Lifetime Members
Lifetime Member
Aug 30, 2006
I'm running a planted African Rift Lake Cichlid
tank in which I have a very hard time keeping up with fish
waste-derived nitrogenous waste even though I run some pretty serious
filtration - just the way things go with Africans' eating habits. I've been following the basics of your Estimative Index routine but I find that, when I test for N (using a LaMotte NO3 kit), my tank
maintains a fairly high level of NO3 (~5 ppm) even without KNO3
fertilization. Given that, I dose very little KNO3 as it does not seem
necessary to maintain good NO3 levels, but my plants still show signs
of NO3 deficiency. I'm fairly new to planted tanks (about 6 months
experience now) and will readily admit that I'm not a chemistry whiz.
Given my tested levels of nitrates from fish waste alone, why am I
still seeing noticeable signs of NO3 deficiency? Am I wrong in not
supplementing with KNO3 at recommended levels? Is there a difference
between fish waste-derived N and potassium nitrate-supplemented N?
I am very curious. Thanks! :)

Tom Barr

Staff member
Jan 23, 2005
Re: A Question on Nitrogen Sources

Well you can add KNO3 for the K+ part, or you can also add K2SO4, which will not add any NO3, but will help the plants use the NO3 that is there.

Most only need to add the KNO3. You can test this with the test kit and see the NO3 fall if the CO2 is good and I assume you add, KH2PO4, Traces and have decent light.

If you have everything esle being added in liberal amounts, then NO3 will be driven down. Try that approach. Then add KNO3 as needed. Plants and AF cichlid both like K2SO4.


Tom Barr