Unknown African cichlids & 7 pleco

Question
I have a 210 gallon freshwater tank. 2 8" Oscars, 2 4" African cichlids (1 is blue striped, 1 is lemon yellow with black on the edges of fins) 4 Bala sharks, 1 6" Eclipse cat, 1 5" Blood Parrot cichlid, 1 small Tiger barb, 1 7" pleco, & 25 Mollies. 2 XP3 filters on the tank, 78F temp, low PH (I use an additive but it never stays neutral) nitrate & nitrite levels are safe, no chlorine, water is soft. 1/2 tank water changes done every 2 weeks, with filter pad changes done every week. The gravel is vacuumed when the water is changed. I feed Aquariun Algae Wafers, 1/2 a zucchini a day, Tetra Color chips, & pellets for the Oscars.

The pleco appears to be taking some abuse from someone, but I don't know who would bother him. I have seen the Albino Oscar "fight" the pleco over an algae wafer. The pleco "won". The pleco appears to have small pieces of skin taken off him, & his top fin has a tear in it. Not bad, but it is noticeable. I have a log in the tank for the pleco to hide in, but he doesn't appear to like it. It's also big enough that the Oscars can get in it too. I'm going to put a cut down piece of 6" PVC in it for the Pleco to hide in, so that he can have an area the Oscars can't get into.

Questions: Who would be taking chunks out of the Pleco's hide, or could it be damage from hitting an ornament that's too small for him to fit into? How can I keep the PH level at the neutral 7.0 they need? Should I keep salt in the water, both for the Mollies & to keep the possibility of infection down for the Pleco?

Answer
Hi Karen:  Do not worry about the pH... so long as it ranges between 6.5 and 8.0 without sudden drops you and your fish will be fine.  They do not need to have a perfect 7.0 pH... In the wild the pH changes constantly.  Keep the salt in the water for both the molly's, cichlids and the pleco.  Any number of your fish can be taking pieces off the pleco... I suspect either the Oscars or the African cichlids or even the blood parrot.  Pleco's are nocturnal so when you give him shelter make sure its a dark space inside... dave