Ok, checking tanks for Ph, Nitrites, ammonia... one tank that had the most recent water change has Ph of around 7, all good with that, other tests fine. Problem is that the other 4 tanks are showing Ph of 6, is this most likely because they are due for water changes or could there be a more sinister cause for such a drop between the tanks??? 3 of the four are 30, 45 and 60 litre tanks, with only 3 or 4 fish currently in residence in each, 4th is 165 ltr comm tank, reasonably well stocked but not over stocked,all tanks are lightly planted, one has driftwood for it's resident Plec. Will do water changes tomorrow anyway and re-test on sunday, just looking for opinions as to cause really, or am i just being a noob???? Anything else i should be looking at or doing??? not wanting to mess around with chemicals, just want stable Ph with happy fish. Thanks in advance