Brown floating scum

I bought a house with a pond. The is pond oval (10x14x3) ~3000
Gallons...the pond has never been clear. It has been green. I
attributed this to the light on UV clarifier being burned out.

Now that spring has come I am often getting brown sludge floating on
top of the water. I can scoop it out but much of it dissolves and
reforms later...also I have not seen much improvement in water
clarity.....

I am at my wits end here is what I have tried to date.

1) I fixed my water clarifier (40W UV lamp)
2) I have cleaned my bio filter (filled 3/4 with aquarium gravel, 1/3
bio-media)
3) I am on my third bottle of Pond Care Algea fix
4) I have put two barley pads near the fountain.
5) I have added an air stone
6) I have added Pond Care pond-zyme and tetra pondclear (bacteria for
pond..these provide temporary relief after pond is "scooped" clean of
sludge)
7) I have added plants (both bottom and free floating.

This is not string algea since there is nothing stringy about it (its
slimey, brown, dirt)

Any tips would be helpful....I am also wondering if a mega (triple)
dose of bacteria treatment would help or could this hurt fish