It is not so much a problem telling them apart from the Garra, Flying Fox, Chinese Algae eater etc. The real problem is telling the 5 different Crossocheilus themselves apart...seeing there are only 2 of them that are true algae eaters (Siamensis and Langei) the other 3 will not eat much algae and prefer fish food. These fish are all caught in the same place so in a tank it can be near impossible to get the 'right' one. Seeing the Siamensis are caught in a different area and very rarely imported your only hope is at finding a Langei.
Siamese flying fox fish in fish tank aquarium
Another species sometimes confused with the Siamese algae-eater and the flying fox is the stone-lapping fish (Garra cambodgiensis). It looks a bit like a faded flying fox, with a heavier body and less color in the fins. The stripe does not run through the tail. This fish will graze on soft slime algae.
Siamese Flying Fox and Goldfish combo
This fish resembles a Siamese algae-eater but with more color. It’s actually attractive enough to be kept for its looks alone. The flying fox (Epalzeorhynchos kalopterus) eats a bit of algae and is related to red-tailed and rainbow sharks. Like the sharks, it’s quite territorial toward its own and similar-looking species, so keep no more than one per community. Adult size is up to 6 inches. This fish and its shark relatives will all graze on soft slime algae.
Siamese algae eater - Wikipedia