You can use a quick fix product like Chemi-Clean to kill the algae, but realize that the algae is there because of poor water conditions. Measure all your parameters and do a few large water changes to fix the problem. And don't overfeed your fish!
I have ordered from them twice without problems. Everything was well packaged and survived. However both times after ordering I noticed a jellyfish in my tank. Kinda wierd.
Any kind of phytoplankton or liquid food mix like marine snow would be fine if you really want to feed them. But be stingy with feeding and only put a few drops in at each time.