Cecil - A long-handle rake might be the best option, all things considered (fish, phytoplankton objective, hard water, etc). Manual removal will provide quick control without excessive copper introductions.
Higher algal-forms (Chara) usually require more aggressive treatments - which may prove detrimental to your phytoplankton objectives if conducted on a large-scale basis.
Do you circulate (as opposed to re-circulate) water through your ponds?
