Need Filtration Advice: please help

I have 7 freshwater fish in a 170G glass tank:
- 10" Leichardti Arowana
- 9" P. Ansorgii Bichir
- 8" P. Endli Bichir
- 6" Tigrinus Catfish
- 5" Clown Loach
- 4" P. Delhezi Bichir

I'm planning to add my 4" Armatus Characin into this mix when it reaches 6-7".

All of these fish each sinking pellets and chopped market shrimp.
I'm running ONLY a Eheim Pro II 2028 (for 158G tanks) but I nightly net out any leftover food and crap out of my bare tank. I change 50% of the water every 2-3 weeks (gotta watch the water bill) and change the filter every 3 months.

I realize I need more filtration, and am NOW under a strict budget, so my question is :

What additional filter (exact model) do you all recommend that will temporarily work for my setup for 6-12 more months (I'll have money to upgrade later)????


Thanks
JJ

Don't have the money or experience to build a W/D filter. Pump would costs at least $150-$200. Any cheap cansiter filters anyone would recommend? With my first child, and saving to buy a house, I don't have much $ anymore.

Thanks for all the replies.

JJ