Hello Lea-Andra--
It's important to realise that no fish (or shrimp, or snail) "cures" algae. To a greater or less degree, all contribute to the conditions that promote algae, i.e., high levels of fertlisers in the water. All animals produce nitrogenous waste (ammonium) which is converted to nitrite and then nitrate by the filter bacteria. These are used by plants and algae as a source of nitrogen when they synthesis proteins. So, the more fish (or snails, or shrimps) the "richer" the water in the tank becomes as far as fertilising the plants and algae go.
There is only one sure-fire way to prevent algae in an aquarium, and that's grow lots of plants.
This works in two ways. Firstly, plants outcompete algae for fertilisers, so the nitrates go into plants rather than algae. Since you want the plants to grow, this is good news. The second thing is more subtle: plants actively surpress algae. In tanks with lots of live plants, even where the nitrates are high, algae just doesn't become a problem.
My own tank is heavily stocked, with a mixture of small but active, high-metabolism fish and a single large catfish. Nitrates can go as high as 100 mg/l/, and yet, there is very little algae. Hair algae is confined to a few strands on dead plant leaves, and the glass needs cleaning
only once every month or two. The "secret" is a mass of rapidly growing plants, in particular things like Cambomba, hornwort, and Salvinia. These actively surpress algae, and are easy to prune back every couple of weeks as required.
There's an excellent article on plants and algae in the Plant forum, here:
http
/www.fishforums.net/index.php?showtopic=106371
As for algae eating fish, there are lots, and I'd go more by compatability and water chemistry than anything else. Scats, for example, are awesome hair algae eaters, but they need brackish water. Flying foxes, on the other hand, prefer neutral freshwater, but tend to favour green algae and brush algae. Ottocinclus catfish eat algae, but they are also parasitic, and will attack larger, slow-moving fish like big gobies, angelfish, and gouramis. A lot of the Garra species are subtropical and need lots of oyxgen, and the same is true for the hillstream loaches. Nothing much eats diatoms, and blue-green algae is completely ignored by all aquarium fish. Snails have a limited effect, though Malayan livebearing snails are a blessing for other reasons, and shrimps will eat algae but their small size and delicateness makes them problematic aquarium residents in some ways.
Cheers,
Neale
