I read my 1st post again. Oh man, it did sound like I am using that multi-stage filter as the only filter. My bad.
The aquarium filter and domestic water filter are 2 separate systems.
The design was mainly to add a constant water changing module to the tank. Which consist of a household RO unit, say set at 5 gallon per day. And an overflow drain to sewer. (or an outdoor planter if there is one)
The overflow is via simple gravity feed. The RO unit works with water pressure in house plumbing.
But towards the end of my post, I started thinking, since I am changing out 5% of the water daily, dirty water is constantly replaced by clean water, could I omit the conventional aquarium filter at all ? Just a thought.
I thought about it some more, now, I think the 5% daily rate is not enough percentage to omit the filter. At 30% RO water daily it may be possible. But that's a big waste of water.
Ammonia builds up constantly as well, filters are running at 200%+ turn over rate per hour to keep up with ammonia. Therefore it is best to have some kind of aquarium filtration system installed.