I have a pleco in a 30 gal, the only other tank mate is a lone zebra danio, these two are the remaining survivors of a very neglected tank that I purchased. The danio seems fine, I did lose an iridescent shark about a week ago, and haven't seen the pleco in over a week, The algae wafers are still being eaten each night but the pleco seems to have gone total nocturnal, to the point that I can't even sneak up on the tank in the middle of the night to take a look for health reasons. At what point should I intervene and make the pleco come out of hiding? Or should I just leave things alone? I did try using a blanket to "black out" the tank and slowly bring lighting back, the danio seemed irritated by this but I still never did see the pleco. Any thoughts?