My daughter wants to set up a "desk tank", salt water, for her boyfriend. We have seen kits selling a clown fish, small anemone in about 5 gal. hexagonal tank. We are being told minimum need is 10 gal, whether we get anem. or not. Same is true for sea slugs apparently. Is there any kind of fish I can get that will work in the smaller 5-6 gal. tank? we are also looking at dwarf puffers. Thanks.