Purchasing a pleco to consume algae in your tank is probably one of the worst reasons to buy one I have to say. Plecos require a varied diet of meat, wood and/or greens. Each species of them can require all three or only one or two of the aforemetioned. To think of them as a sole algae eater is probably one of the biggest fallacies that have been passed by aquarists the world over. Furthermore what algae they may eat will usually only be of the green kind and I have heard possibly brown as well... but I haven't seen that before as a personal experience.
If you have an algae issue you should probably look at your lighting, CO2 and fertilization regime. If any of those three are out of whck you have the potential to have an algae issue. the best way to remove algae is by scrobbing the glass and removing any leaves of plants with algae on them.
