thanks everyone, i am so lucky to have a group of people with oodles of info at my disposal
Anyway, more about my setup; i have 10 fish in my tank...
1 albino oscar named denver
1 black tiger oscar named sammy
1 ell tailed catfish named george
6 bristlenose plecostamos
and finally
1 carydoras catfish named cory (i know how original...)
i have a 50 gallon tank (212L) with a 1200 aqua one canister filter, and a heater, and an airstone.
It's a fairly new setup and last week Denver had a bit of a sulk and didn't eat or move around very much all day but he seemed to heal up by midday the next day thankfully.