Hi Fishy, that link you provided has a great deal of information about how the filter works. It looks like water is sucked in at the bottom of the filter, then passes over the filter material (bio-bag), then spills back into the tank from the top-front of the filter.
The webpage also indicates that there is a flow control knob at the bottom-back of the filter, so hopefully you can prevent having too much current for the betta/ADF
Sounds like a great plan...good luck!
25g Marineland Eclipse (30w T-8 ):
- java ferns, anacharis, corkscrew vals, giant hygros, marimo balls, java moss
- zebra danios (5), otos (2), others TBD
6g Marineland Eclipse (8w T-5):
- anacharis, asian ambulia, java moss
- white cloud mountain minnows (10 = 6-7 inches total)