Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
There are other ways to reduce the NO3 from the tap water before using it in the main tank.
Set up a 'prep' tank that is all sorts of plants, but especially emersed plants.
Make sure they get enough potassium, phosphates and traces, but, of course, do not dose NO3 in any form.
Fill this tank from the tap (don't forget the dechlor!)
Test the NO3 daily. When it is as low as you want to use in the main tank, drain this tank to supply the refill water. If this tank is not very large, then let the NO3 get even lower, then mix this water with tap water.
In the filter of the main tank or the prep tank, use one of those filter inserts that reduced the NO3. They might end up being a bit expensive if you have to keep swapping them out.
Many of us use KNO3 as a source of BOTH K (potassium) AND NO3.
Since you will not be dosing KNO3, then make sure your aquarium is getting plenty of K from some other source. Potassium is a fertilizer that aquatic plants seem to use a lot of. There are several suppliers of fertilizers that package K separately. Seachem Flourish Potassium is one.