Hey i use canna a-b nuets for hard water (im in london with hard water) with canna ph down. I have 1" rockwool cubes supporting my plants in 3litre pots filled with clay pebbles in the E&F table. I usally dont flood my table deep enough to get the rockwool cubes wet but i didnt know it was a problem if u did, but i can see what your saying. But still i add my nuets and they do bring the ph down but i still have to use a little ph down to get it right but then it just keeps rising. im only running like 650 ppm though including the down when i up my neuts will this help stabalise my ph?