Wet/dry compatible with CO2?

Canisters will be fine, but the eheims AFAIK, fill then drain and then repeat, so that would make me think it would help gass out the C02 pretty good (bad thing). Wet/Dry's are usually NOT a good idea with C02, as the overflow, and sump help release A LOT of the C02. Now if you were to make a sump where the baffles were almost level with the next chamber so the water wouldnt fall barely any at all, so there wouldnt be any surface agitation. Also I would suggest a PVC type overflow, not the standard box type overflow. I would just use a canister, basically IMO a canister filter is just like a wet/dry sump, excluding the wet/dry part and it doesnt have an area to stick heaters, or bad fish or excess plants to help with the bioload.

Basically it can be done, but there are eaiser ways.

W/Ds are not a problem w/CO2 so long as the "tower" is covered and does not have airstone(s) under it. The CO2 loss almost always comes from the overflow box, which is highly aerated and exposed to ambient air. The design of the overflow box is critical for CO2 conservation.

I have not used a W/D canister w/CO2 supplement, can't say there with any authority, but the water is not being particularly well aerated by the drain/fill cycle, just the enclosed media being briefly exposed to air.

:OT: What size is the tank anyway, Matak?

Check in the SW/reef forums - I've lost my bookmarks in a major crash and burn. The quiet design is also the CO2-cnaserving design.