Sorry to hear about your coral. That is one of the dangers of having an anemone in a mixed reef tank. If they wander they tend to leave a wake of destruction.
By the pics it looks like you have some problem algaes - most likely due to elevated nutrient levels. IMO your setup will make it difficult to maintain good water quality over time (more on that later). Have you tested basic water parameters lately (ie. ammonia, nitrate, pH, temp, etc.)? I'm guessing that might be part of the issue with your anemone - water quality. IMO your lighting is borderline for keeping an anemone as well. How old is the setup?
FWIW, canister filters and crushed coral substrates are generally avoided on modern reef tanks. They require very frequent cleaning because they trap detritus. Without frequent cleaning the detritus will decompose and cause water quality issues which in turn leads to problems with nuisance algaes and coral/anemone health. The vast majority of reefers today prefer powerful protein skimmers (do a search on the SeaClone - I think you'll find it does not fall in this category), strong circulation and live rock/sand as their primary filtration. For most, the latter method provides better water quality with less maintenance.
BTW, a Hippo Tang is not a good choice for a 50 gallon tank as they grow large and need a lot of swimming room. They also eat a lot and produce a lot of waste which is tough to manage in a small tank. Also, the damsels will likely get aggressive as they mature and cause problems (if they haven't started already).
Not trying to rain on your parade, just offering my opinion. :wink:
HTH