Summer is usually hot with lots of sunshine and this means one thing: algae. Algae blooms are not completely avoidable but a lot can be done to minimize their efforts or shorten the blooms. Check if your UV clarifier is working and make sure your filter system is sized correctly for your biological load.
String algae, which attach to surfaces, is usually a sign of high phosphate levels in the water, which floating algae, which make the water turn green is often a sign of insufficient filter of UV capacity. The beneficial bacteria in your pond and filter can do their job better in an oxygen rich environment. Air injection in the pond or even in the filter can often help overcome those dog days of summer.