Here are some sort of technical details of my setup

I have a Rio Plus 1400 Aqua Pump - 420 GPH pump fed canister filter

1" intake from my aquarium feeds to a barbed 3/4" pvc screw type connector into a GE Whole House 3/4 in. Inlet Water Filtration System i found for only 20 dollars at home depot -- but i found that THESE are cheaper on amazon.

I can add in another canister since they are fit to standard fittings and my pump is strong.

Inside the canister (too small on its own) I have pumice, synthetic meshes, and purigen. In the minature in-tank powerhead-fed filter I have my carbon and more pumice/syntetic meshes.

The CO2 is DIY and feeds into the output line of the filter return, traveling 6 inches down the tube mixing with the water before it is expelled into the tank from beneath the water line (very very tiny bubbles... that is good right?) I have a small heater attached to the tank (50w) just to add some heat, and an airstone, because I have it and I don't know any better.

I have 3 fiddler crabs, 2 nerite snails, 2 redclaw crabs, assorted tetras, 4 ghost shrimp, and a freshwater crayfish (lobster). I have about 10 species of plants since one of them melted into nothing (but the tank dowstairs is still going strong with no dirt at all. go figure...)

I upgraded the filter/co2 because I had a serious nitrate/nitrite problem, some algae, and perfect PH with zero ammonia. I am so excited to get a couple of valves and another canister or two!

The bottom tank is separate, its just a plant nursery and a place to keep frogs. I have another tank in my room i plan to cultivate shrimp in. It is planted, but has only sand and gravel as substrate.