This summer is no different. I don't use chemicals, even though they're supposed to be safe for water plants and fish. My outdoor cats, for some odd reason, prefer drinking out of the pond, rather than a clean bowl of fresh water. There are also squirrels, rabbits and birds that visit, so I prefer to battle this green demon as naturally as possible.
So far this year, after reading that Koi Clay works great. I ordered four pounds from Amazon. I hope it works, but I'm still waiting. I also ordered a roll of filtering material one foot by six foot, and cut it into pieces to fit my filter. It is coarse on one side and seems to be filtering out some of the dead algae, which I clean out several times a day. I also have UV lights, one in my pump and one in my above ground filter. Using a long handled flat net (I'm certain there is a name for it) I dip off as much as I can, but it sticks to the roots and fibers of my floating water plants, and the only way to remove it is to clean each and every plant. I just purchased a new liner, may have to get rid of the plants and everything, but the koi, and just start over.