I have 4 petricola's since the beginning of this tank, 2 years. They've been fine, healthy, they're hiders and don't come out much but I really like them. I usually check my tanks everyday even if it's for a few minutes. Unfortunately summer is a very busy time and I was just doing water changes and feeding. A couple of weeks ago I see 2 of my petricola's are sooo thin. I put enough food in for them because I also have other bottom dwellers(red BN's,and 1 whiptail). My ph is low for them at 6.0, but when I bought them my tank was neutral 7.0 and the breeder said his water was 7.0 too not to worry. All other params are good, 0-amm 0-nitrites and 0-5ppm for nitrates. If it was parasites wouldn't all the fish have problems? the rest of the fish are fine and thriving. They do some weird things like stay at the top of the tank and bob their heads out of the water and rest on plants, all of which they never did. Anyone out there have any ideas what is going on with them please post, thanks. I've posted other places but no answers, also googled and didn't find anything.