I have 4 Syn.Petricolas, they've been in the tank pretty much from the beginning,2 years. Their behavior has changed and so have they. 1. they come to the top and bob their heads out of the water. I thought maybe the water needed more then the every 2 week changes I can do in the summer, went back to once a week changing 30% of a 75g sometimes a bit more. 2 of them have gotten so thin! I was putting down more food for them late at night hoping the other fish were in their sleep mode and would leave it alone. The PH on the tank was 7.0-7.2 when I got them, I know in the wild the ph is higher for them but the breeder I bought them from said his ph was 7.0 and I didn't have to worry. Again that was 2 years ago they've been fine. 2. Now the PH has gone down to 6.0-6.4, maybe the mopani wood caused that? How can I raise the ph naturally? 3.Last year I got 2 super red BNs pleco's and one whiptail, could that be a problem, again I put food in everyones area, in fact I probably put too much sometimes. I feel awful because they are one of my favorites. The other params are 0 for ammonia, 0 for nitrites and 0-5ppm for nitrates, not alot but a good amount of plants, the substrate is pfs and caribsea gravel. I'd appreciate any ideas, whatever I'm doing doesn't seem to be working. All the other fish are fine and thriving.