what kind of algae is it? depending on the type, it could be too little light, too much light, not enough carbon, not enough water changes, too much food, etc. . .
also note that any algae an 'algae eater' consumes just gets pooped right out into the tank. this means more cleaning for you to do overall because of the extra physical waste, and possibly more algae as well if the problem is caused by an excess of nutrients.
plecos won't eat just algae, they need wafers and fresh veggies, and if they don't get those, they will start to go after your plants. they also like to dig, which might become a problem in a tank with no bare ground. most of the time it seems like they poop out more than they eat in the first place.
chinese algae eaters stop eating algae as they mature. they get big and mean, and if they can defend themselves against the barbs, they might go after the barbs - the cae's enjoy eating the slime coat off of other fish, and can stress tankmates to the point of death.
