I have been battling string algae in my pond for the last two years. In my search for a product to remove the algae safely and not harm my koi,plants,or my biofilter. I found the most awesome product. Hydra-aqua crystal @
www.hydra-aqua.us. This stuff attaches it's self to all green algae in pond and cuts off light to the plant. It then drags the algae to the bottom were it can be removed by the pump or by vacuum. After my inisial dose I saw a great difference, and it did not effect my skippy bio-filter at all.I am truley amaized with this product, although it comes from the United Kingdom and takes a while to get here.