70 won't fit over the rim of a 75, you need a 110. Aquaclears are the best HOB
's though, just use 2 sponges and rinse them out when you do partial water changes. Replace the sponges (not both at the same time) when they start falling apart, but they last for years.
I use 2 110's on a couple of my heavily stocked 75's and the 90, the tanks that only have 1 hob
also have a powerhead and an air-driven sponge filter to help circulate water and pick up debris.