We've had the same issue with our rebuild. When it was drained it had quite a rich growth of terrestrial plants on the bottom. It also seemed like the areas near the banks were very nutrient rich and as the pond filled, the FA came on strong.

Things we've done since the first mega bloom, one or more of which seems to have helped: aeration, pond dye, muck reducer and cutrine.

It has receded from covering about a third of the surface to being mostly confined along the banks and corners now.

The liquid cutrine showed results but that was temporary. The granular I put down in the corners seemed to have no effect as far as what was on the surface. The raking works and is also temporary and as far as it appears to me, the muck is drying up and staying on the banks. You can also haul it away if you want.

A couple days ago for fun, a 2 inch trash pump I had set up in one corner to water my gardens I used with a firehose nozzle to mega blast the moss that was stacked up in that corner. I blasted it back down to the bottom.

The algae doesn't seem to produce quite like it was several weeks ago. I'm not an expert by any means but just wanted to share some of the things I've tried.