hi.i have a 36"x12"x18" tank, not sure how many gallons? i was given the tank by a work colleague. not sure how old it is, but it definitely isn't recent. it has a fluvel 3 plus filter (though not sure it's very good). i have 2 clown loaches, 2 black skirt tetras, a red finned shark, a plec, 2 flame tetras. 5 albino tetras? i did have 10 neon tetras, but 5 have died. there is a co2
unit in the cabinet, but not sure what to do with it? as i said, I'm new to this so any advise would be greatly received thanks.