Lots of aquatic plants usually take care of the algae problem but it's usually too many or the wrong kind that one wants. Even if you put the so called right kind of plants in you pond it will most likely change over time into the wrong kind with the plants that are the most aggressive. Even the wrong kind of plants will take out the nutrients of the pond and cut down algae and plants oxygenate, add food and structure.

So to keep the plants down to the level you want add grass carp but you have to get the amount right for what you want by starting slow and watching the results.

With less plants you will have more algae but this can be taken care of with a combination of channel catfish, KOI and Israeli carp. To control these fish from getting out of hand you need some predators.

The other way to achieve the same results as above is using chemicals, airators, artificial structure and feeding.