The easiest way I could put this is that your tank is already full with 1 clown and the rest of what you named. There isn't enough territory in a 10 gallon for 2 clown fish, and even if you get a mated pair, you may still run into waste issues/water quality issues. Wtih all of what you listed I would be expecting to do water changes at least twice/wk.
As for your algae growth, it is true that algae growth is normal... but there comes a time when normal becomes problematic due to size of the tank and what is in it. More frequent water changes, making sure the surface is skimmed at least once/day, keeping feedings light, and keeping the lights to 8 - 10 hrs/day and no more, making sure it isn't too strong... all of these things will help to get it under control. The other big help would be to add as much live rock as you can to the tank. Live rock is your main filtration, and without enough of it, you'll run into problems as time goes on. Is your substrate sand or crushed coral?
Please remember that most animals you purchase are not yet full grown, and knowing how big they get is very very important. You can't fit as many animals into a saltwater tank as you can with freshwater, and the bigger the tank the easier it is to keep stable and the less work it will take to keep it there. Also, remember that a saltwater tank is not considered mature for about the first 2 yrs of being set up, so the period of time before that will mean a lot of ups and downs. Watch SPG/salinity in a small tank like that, too. It will fluctuate rapidly with evaporation, and knowing what it is will help determine whether to add saltwater or freshwater at any given time. Corals, fish, and inverts are all very sensitive to that. Keep an eye on Calcium levels, in small tanks they tend to be depleted quickly, and you will usually need to add liquid calcium to keep things healthy.
If you need any other help, let us know. Good Luck!