Tangs are great if the tank is big enough for them. Reefcleaners.org has a great special going on now for some snails/crabs (check their post for the info about the special). A few items on their site that deal with hair algae:

http://reefcleaners.org/index.php?pa...mart&Itemid=34

http://reefcleaners.org/index.php?pa...mart&Itemid=34

When I am dealing with a problem I throw some snails and crabs at it! Lots of them - I like to use 1 snail and 1 crab per gallon as a general rule. Pick the kinds that deal with the problem that you have along with some other diversity to keep other potential problems from becoming problems. Make sure they are reef safe though.

As for lights - I change them often. T5s I typically go 6-9 months. I watch the tank, if coral doesn't seem to be growing/thriving or if I start seeing signs of nuisance algae, it is time to change them.