pH rebounds to basic, 7.8+ within days
i have very acidic water, 6.2. i'm trying to grow out some plants now and get some jfern and anubias attached to some grapewood. the substrate is half home despot play sand and half gravel, with MTS. the only fish are 3 cories in a 20gal with two 15W and a 65W flourescent fixtures. i have a small undergravel filter plate connect to a powerhead and a HOB that pulls through a sponge, the idea being nondestructive water flow.
so how can i do a 1/4 change and test the pH at 7.0 and the next day it's 7.8. i have another tank with grapewood, and it's pH stable.