Not sure whether I should be concerned about this yet or not, but after my big tank revamp the other day, one of them has dropped its pH from 7.4 to around 6.8 (maybe even 6.6, can't quite tell). Before creating my two different aquariums I had one tank, moderately planted, a smallish piece of driftwood and a small beach rock (tested positive for calcium, but figured it was only small and the driftwood should offset it's effect on pH, which seemed to be ok), pH was stable at around 7.3. The new tank which is dropping pH has the substrate (gravel), plants and driftwood from the old aquarium, plus three other pieces of wood (all off-cuts from the same larger piece which is now in the other aquarium) but no beach rock. Have I overdone it on driftwood? That's the only real difference I can come up with, other than the temperature is now a bit lower 17c as opposed to 21c). Just as a reference, I tested both aquariums as well as the water I use for changes (dechlorinated, left standing for a few days) as a control: Control: 7.4 (tested on high and normal range tests) Temperate tank: >7.4, ever so slightly more orange than the control on the high range. Cold (planted, wooded) tank: 6.6-6.8 They both have the same water, are treated pretty much the same, the only real difference is the extra wood, but I had thought that would take longer than a couple days to affect pH that dramatically?