My Pond is Turning Green?
Make sure that your filter system is operating correctly. The pump should be flowing water through the filter and back to the pond of the waterfall. If the flow is restricted, make sure the input into the filter system isn't clogged and that the filter is clean.
If your filter system, is operating normally, check to see when the last time you changed your UV light. If it has been in operation for more than 11 months, it is time to get a new bulb. Please note: Even if the bulb is still on, if it is more than 11 months old, it's ability to produce UV light at the 264 nm range will have worn out.
If your pond doesn't have a UV light installed, you may want to consider adding one to your filter system to control the free floating algae that cause green water.