My AQ500, on my 15 gal is silent, and works great as a refugium/mini sump. I house a heater,carbon,phos ban and LR with Chaeto. Since the addition this tank has rock stable temp and parameters. I agree it would be too small for a 45gal....maybe use 2 or 1 plus a HOB skimmer, with a couple a PH and you are good to flow
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My CPR (on 90g) works well as any other overflow. I did replace the RIO with a minijet (thanks Christy
). The pump just helps restart after a power outage, the syphon works by gravity mostly. New the CPRs are pricey , better to drill and have a sump if that is an option.
GOOOOOD REEEEFin'