I think this is a problem nearly all pond owners encounter at one time or another. This algae called Blanket Weed can quickly fill an entire pond during the summer months. We have found the best product to kill it is Blanket Answer This product is safe with all fish and plants, and it works! One of the good things about Blanket Answer is it kills the algae slowly over a period of weeks rather than all at once. If all the algae is killed at once the decaying matter can starve the fish of oxygen. You can obviously remove Blanket Weed by manual removal although this can be almost a daily task. There are also fish that eat it these are called Grass Carp although they can only eat relatively small amount and will not discriminate against algae & plants. Maintaining low levels of Nitrate & Phosphate also helps as does the removal of sediment from the bottom of your pond. You may have seen the electronic blanket weed controllers advertised, we have used these and have noticed little if any improvement.