The cylinders are Ceramic Rings. They are used in Canister filters or some hob
's as filter media. They can hold a TON more bacteria than Carbon. I don't know why they would be used in the gravel though. I've never heard of that.
If you can disconnect the UGF
, do it. It is a Nitrate haven and is not as effective as a good hob
. I had them in my 10 and 29 gal
tanks and will never put a UGF
in a tank ever again. Waste will get pulled into the gravel and sit under the plates causing buildup. When you go to remove it, your water will be VERY nasty.
The filters generally don't pick up waste. That is something that has to be done with the pwc
. This is a bit trickier to do with an ugf
than without one.
and WELCOME TO AA REDDERS83!