Wiser souls may want to use those little red lights, drugstores are selling as key chain attachments, to check the tanks in the wee hours. Not only are those lights useful for finding car door key holes at night, but checking fish tanks without panicking everything in sight (where the inhabitants are not supposed to see the red light). The fish may still sense your presence, so be gentle.

In nature, those sleeping locations might reflect relatively safe niches for the livebearers in shallow water. Note how vulnerable they are though, to night feeding catfish with their long, taste bud sensitive, barbels.

That is another explanation for yet another group of mystery deaths and disappearances in our tanks. That new catfish (with the suspiciously large mouth) looks so peaceful and benign during the day. Nights may be another matter. :(

Again, that is why we really must research fish before they become new purchases.