Potasium Carbonate

I have a 240l tank with 6 medium discus 6 botias 18 tetras and a pl*co.
Fairly heavily planted tank with slow and fast growing species at 28C. I
have and UGF with a powerhead which I bubble to remove the grease layer from
the food.  I use peat to lower the ph to 6.8. My water conditions are:

Natural pH 7.2
No nitrite or nitrate.
Supposedly very low Fe,K, Mg and S.

In an attempt to lower nitrate and let my plants grow I am adding Fe, MgSO4
and Potassium Carbonate instead of K2SO4 with the following logic which I
hope is correct.

1.      My natural CO2 level should be 2-3.5. By carbonate hardening this
should shove up the CO2 level.

2.      I need to drop the pH to make the potassium carbonate soluable
(besides being desirable for the discus)

3.      Postasium Carbonate needs to be dosed higher than K2SO4.

Mark Hack