Getting back into fish keeping

The AC70 has exactly 1" of clearance for the rim. I don't know how wide the bracing is on a 75g, and I think that it varies from manufacturer to manufacturer. I would go with the AC70 anyways, it has much more flow and has much more room for media.
 
Thanks, sounds like I will either have to alter my tank (All-Glass, the brace is about 1.2" wide) or go with the Emperor filters and deal with the biowheels off gassing my CO2. Hmmm, decisions, decisions.
 
I think you just got a filter that was too small for your tank. The AC 70 is rated for the size tank you have and should fit fine as long as it is a standard 75 gallon. If it was me I would go as far as to get an AC110, maybe 2. Usually the ratings on the box are not completely accurate. I run an AC20 on my 5 gallon and it's perfect for that size tank, but i do love to over filter.
 
I had gotten 2 of the AC 50's. I wasn't going to run just one filter. Now I'm trying to decide if I want to alter my tank so the AC's can fit or just get the Emperor's.
 
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