Hmm I need one of those filters too.. Azoo Palm seems the smallest, is it discontinued? I don't see it on Azoo's website, only being sold on drfostersmith
. 3" x 3-1/2" x 5", 6 gph, $8.99+$5.99 shipping.
Amazon has the Mignon 60
. 3.2 x 3.8 x 6 inches, 16 gph, $13ish shipped with Prime.
The marina cubus is 5.9 inches long, 5.9 inches wide, 5.9 inches high, so mignon may unlevel it, unless the dimensions are accounting for the to hangover section too... it'll probably also be fine.