It looks like this tank wasn't taken care of that well, but you can fix it all up. What I suggest is that you first get rid of that damsel (black and white fish) because I got one with my setup and it is very aggressive and killed some of my fish. Next I would take the live rock out and scrub off all that algae with a wire brush or something like that because that algae is the worst and a little bit can spread to a ton. But the biggest factor is checking your water parameters with a small $15 test kit and fixing your levels from there.