"Critical Popperian" wrote in message
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Depending on the density of the algae, it could take several weeks
before
you see any significant difference.
If you don't want to wait that long, then by all means add another U.V.
to
the other pump.
You can always turn one off (or both) when the water clears.
It is a good idea to have the U.V. before the filter so that the dead
algae
is taken out before entering the pond.

I can be patient, but do you think this is enough U.V. to control
blooms once it is gone?


I had a 9 watt on a 1000 gallon pond and it took about three days,
not for sure this formula is correct and it probably isn't but here's a
guess,
12 times as much water / 4 times as much uv, just guessing here mind ya
12 times 3 days is 36 days, divided by 4 times the uv would be
around 9 days to clear the pond. Variances could be water flow
through the filter and who knows what else.
I would say it would be much harder to remove the algae than to
maintain control of it, especially with a good supply of plants in the
pond.