The Chinese Algae Eater is nothing but trouble. It grows to 6 inches and almost always turns very nasty. It does not eat algae as it matures. It is documenteed to eat the slime coat off various fish.
The common pleco attains anywhere between 12 and 20 inches (30 to 50 cm) and requires at minimum a 4-foot tank. It has a very high impact on the bioload (so does the CAE for its size). Most people buy these intending them for small tanks, and the fish suffers as it grows (if it survives).
This hobby has a serious problem, and that is lack of knowledge by most who work in stores, coupled with a reluctance by some to do proper research before acquiring a fish. Knowledgeable staff could at least help the latter, but many of them know little more than fish live in water.