I know most here suggest plants and more plants, but Algae hits here way
before the plants are growing in the spring. I put in a 57 watt Aqua
clarifier and in two days the pond was crystal clear. I was truly amazed
since the bottom still had leaves and some trash from the winter. What's
great now is that the dead algae seems to just fall back to the bottom when
I fish around getting the trash off the bottom instead of clouding up the
water again.

On thing to note on the uv clarifiers is that you need to make sure they're
turned off when the pump isn't running. The water circulation is what cools
the bulb. So I put a switch that turns both on/off at the same time (just
put the switch on one A/C outlet).

Plants are great, but if you're impatient like me, the uv is the way to go.
And since the bulb last 14 months at a cost of apox. $50, it's not much more
than chemicals.

Scott