Planted Tank Guru
Join Date: Nov 2009
Location: Missouri united states
My only concern would be the drop from pH of 8+ overnight, to 6.
Perhaps clay from fluorite ,and or any peat that the soil might contain is somehow adsorbing carbonates.I am not sure this would happen that quickly.
While this would be of no mind for plant's,I would be concerned from fish perspective with the sudden change from source water with pH of 8 + at weekly water change down to pH of 6 that quickly.
While fishes can handle gradual shift's that take place each day,they may or may not appreciate this sudden change overnight.
I would be tempted to perform smaller water changes as opposed to large 50% or more changes if test result's are to be believed, and no measures of adjusting the water are being performed by you.