Algae-eaters

Algae-eaters visible and invisible. If your green meadow were growing tall and rank, rather than using a flame-thrower you might turn the sheep out to graze. Besides the visible algae-eating fishes and invertebrates, there are a host of microscopic grazers in the plankton and among the biofilm. Encouraging zooplankton is really what keeps the water clear and algal films under control.
 
About "algae-eaters." Certain fish have an appetite for algal films and over-mature plant material that's going soft. (Certain fish have notorious appetites for un-softened plant leaves, too.) Each species has preferences. It generally takes more than one kind of algae-eater to control the full range of algae in a tank. Your experience will show you which combinations of species are competitors for similar kinds of algae and which complement one another in their algal tastes.
 
The SAE, or Siamese Algae-eater, is Crossocheilus siamensis. It has some attractive but less useful Epalzeorhyncos relatives plus an oafish imitator, the "Chinese" Algae-eater, Gyrinocheilus aymonieri, which you may want to avoid; before you make a hasty purchase, look at the unvarnished report on Gyrinocheilus, with photos, at the Aqualand (Des Moines IA) website.
 
The algae-rasping Otos, various Otocinclus spp, are very helpful and endearing miniature Loricariid catfish. Many other Lories (Loricariid catfish) depend on algae, especially the young ones. But as they grow, the larger ones, like the Common Pleco, lose interest in algae and start mindlessly trashing plants.
 
Lately folks have embraced the slightly snappish and aggressive cyprinodont, Jordaniella floridæ, the American Flagfish. I have no personal experience with it. Many other herbivorous fish, and omnivores such as Barbs, will pick pick pick among the algae all day long, without having much effect on it, however.
 
About algae-eating shrimp. Takashi Amano introduced us to shrimp for the freshwater aquarium. He is convinced that algae are being kept under control in his immaculate, richly-planted tanks by algae-eating shrimp, which he chose after an exhaustive selection process he described in one of his books, which reminded me of the next-to-last chapter of Cinderella.
 
Surely Caridina japonica, the "Amano" shrimp, are supporting themselves on algae and detritus, and preferentially on any available flake feed, it appears, but I think it's the vigorously-growing plants that outcompete algae in Amano-style aquaria. Planted aquaria like Amano's always have plentiful algae-eating plankton life too. My old wish that  genuinely tropical shrimp from freshwater habitats, rather than Caridina shrimp that really need fairly cool brackish waters to thrive, were consistently offered at my local LFS, has been granted during the new century's first decade.
You'll find what information I have about freshwater shrimp among "Invertebrates" rather than here in the Algae Combat Zone.