you build a Co2 reactor to be hooked up inline sort of like
this
when i had my C-220 i really liked it that was back when i could get them off ebay for like 80shipped now there more expensive. the thing with them is they have vary tight interlocking basket which mean almost no water bypass also thay are easier to prime because thay have a priming button. the SunSun basically the same product but much cheaper and i know CWO4GUNNER likes them (coming from im thats something). here is his review of
them.