Everyday Systems

This is really OFF topic! DH and I dug a garden pond last September. We put in lots of water lilies and other water plants. We only have 12 fish, so it's not over stocked. Our pond is 14,200 liters.

This spring our pond water is pea green soup. I cant see more than a few inches below the water surface.

We bought a new filter that has UV to kill the algaes, but it's not helping. We've changed 1/4 of the water, no help. Our fishies are starting to die.
We oxygenate the water both with an air pump and a waterfall from the filter.

Does anyone have any advice or help that won't cost a fortune?

My dad has ponds in his back yard. He says he has to just clean them out fully every year or two. Like, actually drain all the water out, scrub down the liners, and then put everything back.