Low nitrates, what to do?

[fresh_newby]

I have recently started adding KNO3 as my tanks were getting next to no nitrates (low stocking levels). And it has been a wonder for me. The extra K (potassium) is really useful as well. I would agree that if you are ordering from Greg Watson (a good choice) then grab the phosphate and trace mix as well. The balance of ferts should be 10(N) to 1 (P) to 10(K) or there abouts.

I bought my KNO3 locally at a hydroponics store, super cheap for the amount you get. If you buy dry powders you can either mix it when you are using it or make a stock solution. If you make a stock solution then I suggest keeping it in the fridge and making up smallish amounts at a time.

Don't forget to dose K2SO4 for additional Potassium source. KNO3 is not enough.

 

[TKOS]

KNO3 is plenty to add K since my tank is so lightly stocked (1 fish). In a heavily stocked tank dosing the extra KNO3 will just lead to a high NO3 level, which the K2SO4 will help prevent.

 

[fresh_newby]

I am not saying you don't dose enough KNO3...I am saying that dosing KNO3 enough isn't enough Potassium for your plants so you have to supplement it with K2SO4

 

[TKOS]

Thanks. But my Potassium problems have been solved with KNO3. So for my tank anyway, KNO3 is enough. Extra K will only be needed if I substantially up my NO3 load to a point that my plants are seeing a lack.

 

[plantbrain]

KNO3 and dosing via fish waste and K2SO4 are quite different.

One version starts out as organic N and then urea and NH4.
These can lead to algae(especially with higher light) and why we cannot keep adding more and more fish to supply N in higher light/CO2 enriched tanks.

The other starts out as NO3 and is taken up.
KNO3 has a positive impact on the O2 levels.
Organic N from fish has a negative one.

Now at lower light, or non CO2 tanks, the rate of N uptake can be matched with fish waste.

But.......you do not have to do a non CO2 tank that way either.......you can add KNO3 and not have a high fish load.

Likewise with a CO2 enriched high light tank, you can have a good sized plant and fish load, an top off the needs with KNO3.

I had a client who had 14 discus full size well fed and other cories, cards etc in a 120 gal tank, by most folks' standards, this was a packed tank.

About 50% of the N came from the worms/food etc, the other 50% came from the KNO3. He still did not require K2SO4, see the KNO3 sticky here on AC.

This was at 220w PC lighting (A&H supply) of light on a 120 gallon tank with CO2.

This amount of lighting was more than enough, by many's standards, relatively low lighting. He is able to grow any plant he wants and the tank looks super.

Now you can add more and more fish and food etc and have less plant biomass if you are willign to do more frequent and larger water changes.
One SFBAAPS member has massive fish loads with Java fern, no CO2 etc, but he has an auto water changer that does 30% daily water changes.
One feller added NH4, about 0.5ppm per day but also did 80% water changes daily.

It can be done, but the trade offs might not be acceptable.
Therein lies the utility in trying many methods once you have mastered one method.

You know what each has to offer, why it works and the limitations.

Regards,
Tom Barr