Silt?

It may be the lime precipitating out of the water. If the water had a high Ph or there are fresh concrete ornaments or mortar about, the lime can easily be washed into the pond and then precipitate when the concentration gets very high or as water evapourates off surfaces leaving a sediment the same as in a kettle. If this pale brown layer of 'silt' coats the oxygenators in a brittle film then that is what it is.
A pond vac will sort it out, but unless you want a constant battle against the nature and the fundamentals of this planets physical laws, I'd wait to let it sort itself out. Anyway the blanket weed will soon clog up the pondvac.
It may however be the case that the pond needs a good slooshing down with silglaze or poolglaze in order to drag some of the lime out of the surface of the concrete. In which case it would be an idea to empty it out, paint on the silglaze and then wash it off, do it again and wash it off, and then fill it up. That's a bit of a parlez vous at this stage.
Get them plants in there, and top up with rainwater in future if you can. In three months time the bottom is going to look like mud anyway.
Patience and the pond keeper should be close friends and walk everywhere hand in hand. That is until there is an emergency and then you can call up PANIC.