|Common Plecostomus, Lynn Smith Photo|
Plecos are an unusual fish - fans of plecos are few and far between, and yet they are ubiquitous in both the industry and the hobby. They are renowned for the habit of juveniles of the species to be voracious consumers of awfuchs - the algae that cakes onto items in the tank. They are usually kept for just that purpose, with their owners having no idea how large they get as adults (we're talking a foot or more), or that their eating off of the glass diminishes with age. A few keepers keep them because of what they are - big, placid armoured catfish.
I'll be the first to admit that's actually pretty cool, but I'm learning I have a soft-spot for large catfish.
At any rate, it's difficult to talk about the ideal conditions to raise plecos, because there are, as I mentioned, quite a few species that are all slightly-different. There are, however, a few general rules. The depth and volume of the tank is not nearly so important as the length, and the longer the better - an adult should be in a tank no shorter than 4 feet and should have about 50 gallons of "breathing space". The adults eat wood, rather than algae, of which mopani is preferred - real drift-wood should be present in their tanks at all time as both a digestive aid and a decoration. They prefer dim lights with places to hide. Aquatic plants will usually get eaten, but consider surface-plants. They prefer quite a bit of flow and high oxygenation - if I was doing a dedicated river-fish tank, I would consider a bubbler and use a power-head for flow.
These fish are amazonian. They prefer corresponding temperatures (in my experience, they are quite happy at around the 79 degrees F mark, though I've heard anywhere from 70 to 80, water that's relatively soft (5-25dH), and a pH in the neighbourhood of 7.2, though they tolerate everything from 6.5 to 8.0.
I've had some success feeding larger plecos blanched zucchini in addition to their regular diet, but this breaks them pretty quickly of their cleaning habits.
There are, of course, more interestingly-coloured and exotic species of pleco, that carry more cost and correspondingly more or less difficulty in handling.
But wait, you say: My pleco is doing just fine in a (10, 20, 30, etc) gallon tank. Okay. I'll believe it. When you're considering replacements, however (he'll either stunt or get to big, trust me), consider Ancistrus spp., or Bristlenose Plecos. They're smaller, and never lose the algae-habit. Plus, their little bristles make them look cthuvian, and that's always a plus.