However if the green persists, it tells us there is an imbalance in the pond ecology. The solution to that is to fix the imbalance. While some pond keepers would have you chuck in some chemicals, the reality is these are merely band-aids and won't “solve” the problem, they'll only mask it. If you want to solve the problem consider the sources of the problem.

Many ponds have too many fish in them. At one inch of fish per one square foot of pond surface, you can either have three big ones at 10-inch length or 30 little ones at one-inch length. (note that 3 ten-inch fish will likely give you 100 one-inch fish every year) If you have a greatere fish population than this, understand two things are happening. The first is the pool ecology is being upset because of too high a level of fish excreted waste and high fish populations are likely eating the oxygenating plants that deal with this excretion waste material. The real solution is to lower the fish population. I note if you have fish and are feeding them, the other recommendation is to stop feeding or to drastically reduce your feeding. Excess food creates excess waste which in turn creates green pond water.

The second solution is to increase the oxygenating plant level. A rule of thumb for doing this is to add one bunch (10 stems or so) of a floating oxygenator plant such anacharis for every 3 square feet of pond surface. Reducing the fish population and adding the oxygenators will clean up the algae in few days. If you add oxygenators without reducing the fish population, the fish will likely eat the plants and the green pond water will not go away.

Understand there is not magic bullet here. You have to get that ecology in balance and the way to do that is to follow a few simple rules to control fish and plant populations. The two thumb rules above will solve most algae problems.