Planted Tank Guru
Join Date: Jul 2010
Location: British Columbia, Canada
There are of course many options. Many use either canister filters, or HOB's, or sponge filters, or a combination of these, with great success.
For keeping discus though, quite a number of hobbyists shy away from using canisters, as they are generally more time-consuming (for fairly frequent cleansing/maintenance), but rather prefer using HOB's or Sponge filters, for the ease of maintaining them well, and the ready ability to interchange/vary/ and refresh media.
(keeping in mind that for those using canisters, the tendency is to clean them less frequently than other types).
In my 75 gal planted discus tank for example, I use 2 AC 110 HOBS, which I find are terrific for easily maintaining well and producing good water quality.
I swear by them, and wouldn't use anything else.
You could consider that, or use one 110 and one 70, or even 2 - 70's.
A couple of large sponge filters would be fine too, but detract from the aesthetic looks of the tank, imo.
Use whatever you prefer, but no matter what you select, get a filter or filters that is/are rated for a much larger tank than 75 gal, so as to significantly hike up the water turnover rate.