Ancistrus includes the bristle nose plecos, right? Usually those are OK for planted tanks, but if you are having trouble you may have to move them to another tank or get plants that they won't eat. I had the same problem with my Rubber Lipped and L145 plecos, and I eventually had to move them into a non-planted tank. My swords were the first to fall prey to the plecos, I think because they have a larger surface area that accumulates algae and microscopic goodies; in the process of eating that stuff, the plecos just incidentally rasp off the outer surface of the leaf, which will eventually turn brown and die. I watched them do it for a while before I realized what was happening, and they did not look like they were actually eating the plants.