Thanks for the replies. Makes sense about not adding anything to the water (though I understood Baking Soda to be the accepted way of raising KH without affecting other parameters).
Rex, I think you misread my numbers though - PH is 8 out of the tap, KH is 3.5. We use baking soda to raise the KH.
We figured altering KH would be less detrimental to the fish than major PH swings with water changes.
As for fluctuations, I don't think it is - we just haven't tested the tap in a while. We've got some sitting to test tomorrow.
72g bowfront, 4.5 wpg (4x65w 48" + 1x65w 24" Aqualights), 100% Eco-complete, Eheim 2026 & 2213, Pressurized CO2 w/JBJ Regulator & Milwaukee SMS122 pH controller, TurboTwist 12x UV Sterilizer
30g, 4.6 wpg, 100% Eco-complete, Eheim 2026, Pressurized CO2 w/Milwaukee regulator and SMS122 PH controller, Turbotwist 6x UV Sterilizer
16g high, 4.6 wpg, 100% Eco-complete , Eheim ECCO 2231, Hagen Nutrafin CO2, TurboTwist 3x UV Sterilizer
JBJ Nano-cube 6 - quarantine tank for now...