Ok a few of points:
Firstly you are probably going through the normal algae cycle near enough everyone gets with a new saltwater tank, there are plenty of threads on this in the saltwater section of this forum, but basically decrease the nurtrients going into the tank (use RO water), add a cleanup crew, increase export of nutrients from the tank (grow and harvest macro algae, add a protein skimmer, increase water change frequecy), and just wait it out.
Secondly as has been said in another thread you made in the saltwater section, 7 gallons really isnt big enough for a fish long term, both in terms of size and keeping the environment stable. I would definatly consider upgrading to at least a 20 gallon tank.
Thirdly, damsels are generally very aggressive and not a suitable tank mate for a clownfish in a nano tank.
He has saltwater fish in an extremely small nano tank. Cleanilness will be next to impossible.
It is possible to have very clean nano-tanks as long as stocking is sensible. Just look at www.nano-reef.com