Pond Bacteria can be very helpful when used appropriately in fish ponds. But no additives or UV lighting is a substitution for proper pond filtration.
Using chemicals, UV lights or bacterial additives to control algae, is like using bandages, covering up a much more dangerous, underlying cause of the green water.
The usual cause of green water, other than environmental changes that throw bacteria colonies out of sync, are undersized biological filters and/ or the pumps that run them. The bacterial colonies are not large enough to handle the breakdown of nutrients that algae feed on. So the algae flourish, while you don’t get to see your fish.
I will explain the reasoning behind this at a later time but the basic principles behind the issue are-
Overfeeding- adding excess nutrients to the pond.
Undersized filters- the filters are too small even if the fish are never fed.
Poor Maintenance- skimmer pads must be cleaned and excess organic matter removed from the pond.
Under sized filter pumps- If the pond has inadequate circulation, even the largest filters you could possibly install with not be able to do their jobs.