Hi Allen, not sure what it is you need to know....I use AC filters on all my tanks; the larger ones, used to be AC 500...some smaller, AC 110, now the #s are changed, just confuses me, lol......put sponge pcs on the intakes & the large sponge that comes with inside....I love'm...in addition, each tank has large sponge air-driven filters....together, this seems to be all thats needed...anytime I test, all is ok..if I use extra sponge filters, there's always one at the ready for emergency situations....JMO,
Dottie