Chinese Algae eaters, when young, are terrific algae eaters, even eating hair algae. As they get older though, they can become territorial, 10 inches long and very hard on guppies. They will not swallow them, but may really suck on them, causing wounds, infections and tattering fins.

Please note that Flying Fox is Epalzeorhynchus kalopterus. The Chinese Algae Eater is Gyrinocheilus aymonieri. They are quite different fishes!

There is also the SAE - Siamese Algae Eater, Crossocheilus siamensis which is perhaps the more efficient of the algae eaters. It can be confused with several of the others. All of these fishes are South East Asian Cyprinids and to a degree they all eat algae. There are other Asian (and American as far as that goes) minnows which eat a lot of algae. I've mentioned the central stonerollers (who of course, rock.)

Please also take a look at http://www.thekrib.com/Fish/Algae-Eaters/

Many of the fish in your aquarium will eat guppy fry. If some are really hungry, they might eat slightly larger guppies.