MBOU said:- 3 products that works great in the HOB filter... Evolution Aqua Pure balls (fit in by the flow adjuster), Polyfilter (not cheap and aimed at marine but if you cut tiny cube and put it in by flow adjuster... it strips out EVERYTHING bad) and last but not least... the Greenex 'teabag'... really does help with algae (though Polyfilter does this too...).
I use the Evolution Aqua Pure Pond balls as you get more for your money than the Aquarium version, the only difference is that they are black vs clear. In your filter you cannot see them anyway
Can you explain more about the Greenex teabag as I have not heard of this before?