I have 2 3in plecos that are starting to grow. they are very healthy and active. They eat leftovers and driftwood. The other day I noticed some white stuff on one of the plecos and today its gone. Now I notice that there is some white stuff that is trappped in my filter screen. It loks like the pleco is shedding. I know plecos had no scales so does it shed its skin? I have added salt in the tank. Did I add too much or is this normal?