I have a Prizm, which is on my 45g. It is the smaller one, I think it's rated for 75 or 100g, not exactly sure. I like it, I think it works well enough for the size of my tank. I think it would be way too little for a decently stocked 100g. It is reasonably easy to adjust after each cleaning, and I haven't had it leak all over everything. I've had no problems. They do make a "deluxe" expansion set or whatever they call it, which includes an overflow so that it is skimming stuff from the surface, which I would recommend. I don't have it, and I have to keep the water level kind of low so that it doesn't make a film.