I was going to respond earlier right after you posted the question, but I obviously hesitated. Yes its a small skimmer and yes it the manufacture may say it can do a 90 gal. However, if your bio-load is small enough then you could use this skimmer. If you do so, I would definitely make sure you drill the collection cup and drain it into something bigger. Again as you know... I think it would all depend on your bio-load.