Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
I sure would not break up or crush the tablets.
Put the tablets on the floor of the tank before adding the substrate, or else press them in through the substrate until they touch the bottom. I would put 3-5 around the Sword depending on the size of the sword, and maybe space them about 6" apart if the tank is heavily planted, or 1-2 per plant if it is lightly planted.
K2SO4: I have only ever used it as a dry dose or wet as a water column fertilizer, never in setting up a tank. If you want to try it maybe a very light dusting on the floor of the tank, but still able to see through it. Part of the problem is that adding sulfur to the lower regions of the substrate might contribute to H2S that can happen with low oxygen areas. If you had a different source of K that might be a better option.
If the fish food is already keeping the NO3 close to 30 ppm then I also would not dose N or P. Fish food also seems to have enough phosphate, if it has enough N.
Today's test showed dropping KH, so I added baking soda, and rising NO2 and NO3. I may have to do another water change to get that NO2 lower. :-(