I recently was given an older (28 years, really) 55 gallon Plexiglas tank. Even before I got it, there was always a problem with algae on the glass. I got some reef janitors hoping they could keep up with it, but most of the snails died in the first week. The tank has been set up for about seven years. It’s inhabitants are reddish purple mushrooms—many of them, they seem to be doing very well; a lettuce coral (I think) that is just holding on; an anemone; some snails and hermit crabs, no vertebrates. The algae are a film of brownish red, and green, and are very hard to get off. Where should I start? Thanks!