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?