I have a biocube 29 and have two clowns and a dottyback. IMO
it is over stocked. If I was u, I would go with smaller fish. Like neon gobies or shark nose gobies. Citron gobies. While these fish can be ify (sometime dont last long). You might be able to have three fish without cyano
and other algae problems. I have added a 20 gallon fuge to finally clear my tank. Just my opinion. Also I would skip the protein skimmer if you have thought about it yet. If you keep up with water changes you will be fine.