I've had a 75g FOWLR tank before with a Volitans lion and a trigger and a snowflake eel with no skimmer. I used a Fluval 404 and did small water changes every other week. Tank was crystal clear and the fish were happy. I have a 25g reef tank that has been running for over 3 years and I don't have a skimmer in that tank either. In fact there is no filter at all. Just a ton of live rock, live sand, lots of corals, 3 fish and inverts. There are three pumps in the tank for circulation and i do small water changes in that tank every few weeks. That tank is also crystal clear. I think your brother would be fine without a skimmer, as long as he has a good filter. Good luck!