worried something bad is in my tank.
Been noticing at night my fish are all sleeping in the same (fairly large) cave.the tank is 20 us gallon (getting upgraded to a 30g next month) and my fish now a small ywg, tailspot blenny and a black bar chromis are all sharing the same hidy hole. I had another chromis it disappeared and my clown go by vanished weeks ago (was living in the sump and only came out during feeding now no where to be seen). Clean up crew are still alive minus a few hermit craps which are fighting over the same shell.
Just wondering what would be the best way to find out whether something is in the rock.