Pottsy - I'm unaware of any other fish specie (coldwater or otherwise) that would be an effective deterrent to filamentous algae. Tilapias, with their very prolific lifestyle, provide an excellent forage-base and some algae-thinning benefits. But, a low tolerance to relatively mild water temperatures and stocking-containment requirements (they're an exotic specie) are definite drawbacks for Tilapia.