Basically I have a pond which is fine, clear as glass really and no UV
filter on it. It isnt a very large pond as far as they go but its all going
great....

My mothers pond on the other hand is completely green with suspended algae.
She has a larger pond than I do. Before she had a small filter which had a
UV light in it but we swapped it for a larger filter without UV.

Yesterday I fixed it so that the pump is pumping to both the larger filter
and the small one with the UV lamp in it. How long should it take to become
clear? I've heard that you need to replace the UV bulb every year, should I
do that today?

Since it is very green should we empty out some or most of the water and
start with fresh tapwater to give the UV lamp less to do or just let it rip
on the super green water?

Poor old mum is getting a bit stressed out.

Many thanks for your help,

Regards,

Dan Bowles