That's not true it needs to be turned on 24/7 to stop the bloom in the first place from building up
It's called putting stop to the problem before its visible
Anyone who buys a uv only to have it stuck in a cupboard or switched of is crazy
It does more than kill green it keeps parasites at bay
You get 2 types of uv
A uvs which is the type used in tanks uvs = ultra violet steriliser
A uv for a pond is a uvc ultra violet clarifier
They are both make to work different
A uvc would be way to big for a tank and only clears green
A uvs which is what everyone buys for a tank is designed to kill green and kill parasites in the free swimming stage
If you have the flow right a uv will kill parasites in the free swimming stage
The tank type should be run 24/7 FACT
Please don't try to tell me about uv I have been running them for over 25 years