[BryceM]

I have a 180g aquarium with a 20lb CO2 cylinder setup. The best method of dissolving and distributing CO2 in an aquarium this size is debatable, but I don't think you'll get what you're looking for by adding it to a single canister filter return.

In my tank, to reach desired levels the CO2 runs at a steady stream of bubbles. I use an 18" long 3" diameter DIY reactor made from PVC. In a simple canister filter return there isn't time to allow for proper dissolution of the gas. BTW, most people would run the CO2 into the inlet of the canister, not the outlet, unless you're adding it to a reactor.

I'd recommend either a series of diffusers or a reactor of some sort. If you have lowish light levels, a relatively low CO2 level might be good enough. In that case, it really wouldn't matter how you do it. Anything else though will require a well thought-out system.

Where I live a 20lb cylinder refill is around $25.

 

[BryceM]

By DIY, I meant that the reactor is a DIY reactor, not that I use yeast fermentation. I have two aquairums with CO2, both with pressurized systems. I messed around with yeast CO2 long enough to know that I lacked the time & energy to keep it going.

If you bubble the CO2 into the inlet, the pump impeller helps to break the gas into small bubbles. It also has more contact time. This method works better for smaller tanks. Feeding a filter as much CO2 as I use would probably result in vapor lock.

Honestly, for a tank that size my strong preference is for a reactor. They add almost zero resistance to the system and they're highly effecient.

I don't have any experience with the needle wheel pump that Orlando is recommending. They're more commonly used on reef systems but from what I can see, it should also work well.