I agree with Dan. Just siphon the bottom during water changes, most any clean up crew will be a lunch buffet for that group. I would also tell him to get a bigger tank, soon. The fish he has now are probably teeny tiny small. But Triggers grow fast, as do bettas. A humu-humu trigger (which I am assuming is Rhinecanthus aculeatus) can get about 10- 12 inches long. A marine betta will acheive a max size of 8-10 inches. The lionfish is probably a dwarf lion and will be fine in a 30, but if It is a Russel's, Volitan, or some other species of large lion, then it will need a bigger tank also. Keep in mind that the longer he goes with these guys in a tank that small, the more nasty the waste will be. As I said, triggers grow very fast. The marine betta is a species of grouper AFAIK and will probably grow rapidly also. As the fish get bigger, their waste will get bigger, and the more food you will have to feed them, and as mentioned, they are messy eaters. He better have one massive skimmer on that little tank if he wants to keep them alive for very long. I would venture to say that in less than a year, he will find himself out of space.