Most of the experts on this forum will tell you the only way to reliably control weeds/algae over the long term is to reduce nutrients going into the pond.

However, that's far easier said than done. My pond had the same issue as yours and there's a cattle ranch across the pond so I assume that manure from the cows was causing the nutrients and thus causing weed/algae growth.

There's nothing I could do about the cows -- I cant afford to buy the ranch out and I sure as hell can't tell the ranch owner that he can't let his cows go to the pond so I was stuck using other methods.

This is what I did:

1. Mizzen copper algaecide appied to 1/5 of the pond every 2 weeks until the entire pond was treated.

2. Added 2 aerators

3. Supplied grass carp at 3 per acre

4. Manually raked/removed the worst areas.

With all 4 of those methods I managed to reduce the weeds/algae from 75% coverage of the pond to zero on the surface and about 10% submerged on the bottom.

I'm sure it will flare up again at some point in the summer and this coming summer I'm going to be a lot more aggressive about manual removal before it becomes overwhelming