Welcome to AA!!
As an advisor I must advise you that your tank, if this is the 30g that is in your profile is way overstocked...
I am sorry to be the bearer of bad news, but you will probably loose alot of your fish if you do not upgrade or get rid of some of those fish.
I count 9 fish just in the pic.
In a 30g tank you sould not keep any tangs, or angels at all.
Sorry for this info on your very first post, but I thought you should know.
How long has the tank been set up?