UV is 100% effective in clearing green water when used correctly. Correct flow, bulb still powerful enough, glass sleeve is pretty clean, etc... Since you have the UV already and sounds like you don't want green water I'd fired it up. Don't worry about removing the killed algae, it will decompose on the bottom. Vacuum if you like.
As to why your pond turned green...no one knows. Lots of species of algae, and science hasn't even for sure decided on whether they are plant, animal or bacteria. We know very little about algae life cycle. Given limited info people often draw conclusions that don't generally hold up very well. Here are a few favorites...
Green = photosynthesis = sun. If your pond is green it must be getting too much sun. Yet there are millions of ponds and bodies of water in full sun that are not green. And in full dense shade there are many that are green.
Green = nutrients. Yet virtually every single crystal clear on the planet has higher ammonia and nitrogen levels than every green pond. If you test your pond I'd be betting zero ammonia and zero or very low nitrogen. I know this because you pond is green. That means conditions allow for algae growth and they consume all ammonia and nitrogen as soon as it becomes available. When your pond clears ammonia and nitrogen can increase...a lot. So if ever there was a time to test ammonia it is when you do something to clear a green pond, like turn on a UV. Algae consume ammonia directly so bacteria that convert ammonia don't multiply as much and when the water suddenly clears there's a little while (few days) when ammonia consumption is low and it can build up.
Temperature = spring = green. Yet many ponds stay clear all year, for years and years. And many ponds stay green all year and stay green for years and years.
Balance = ??? I don't even know what that means other than if your pond is what you want it must be in balance. A green pond is every bit as natural as a clear pond...maybe more so. We generally push ponds to be clear.
We do know, thanks to Norm Meck, that clear pond water often (we don't know percentages) contains a chemical that kills green water algae on contact. A poison if you will. What produces the chemical isn't certain, Norm's theory was a bacteria produced it. My theory has been it's produced by other algae, bigger algae like string algae, based on my own experiments and also that this type of behavior is common for organisms (allelochemicals). It's been seen in saltwater algae but freshwater algae hasn't been studied as far as I can tell. There is evidence coming from aquarist using string algae but they seem confused on why it works. Still, best theory I have.
What this all boils down to...
UV is 100% effective when done right, but watch ammonia. Often UV can be turned off after a week or month as string algae (macro algae) starts to grow. And you may never need to turn it on again. Then you'll want to know how to control string algae.
Trickle Towers and streams can be very effective because they give string algae a place to grow where they can get more sun, O2 and over come the defenses produced by the green water algae.
24/7 drip water changes can be effective. It basically flushes alway algae faster then they can reproduce and also gives string algae a better chance to grow.
Beyond that there are dozens, maybe hundreds of "cures". Magnets, barley straw, salt, bacteria, phosphate binders, etc... It's endless. And I'm pretty sure if any of them actually worked there wouldn't be hundreds of "cures".
That brings me to the point...be careful of the internet. I've seen more ponds filled in by people after trying dozens of "cures" promoted online and feeling like failures. #1 reason more people don't keep ponds are the pond "experts" promoting silliness online.
As to why your pond turned green...no one knows. Lots of species of algae, and science hasn't even for sure decided on whether they are plant, animal or bacteria. We know very little about algae life cycle. Given limited info people often draw conclusions that don't generally hold up very well. Here are a few favorites...
Green = photosynthesis = sun. If your pond is green it must be getting too much sun. Yet there are millions of ponds and bodies of water in full sun that are not green. And in full dense shade there are many that are green.
Green = nutrients. Yet virtually every single crystal clear on the planet has higher ammonia and nitrogen levels than every green pond. If you test your pond I'd be betting zero ammonia and zero or very low nitrogen. I know this because you pond is green. That means conditions allow for algae growth and they consume all ammonia and nitrogen as soon as it becomes available. When your pond clears ammonia and nitrogen can increase...a lot. So if ever there was a time to test ammonia it is when you do something to clear a green pond, like turn on a UV. Algae consume ammonia directly so bacteria that convert ammonia don't multiply as much and when the water suddenly clears there's a little while (few days) when ammonia consumption is low and it can build up.
Temperature = spring = green. Yet many ponds stay clear all year, for years and years. And many ponds stay green all year and stay green for years and years.
Balance = ??? I don't even know what that means other than if your pond is what you want it must be in balance. A green pond is every bit as natural as a clear pond...maybe more so. We generally push ponds to be clear.
We do know, thanks to Norm Meck, that clear pond water often (we don't know percentages) contains a chemical that kills green water algae on contact. A poison if you will. What produces the chemical isn't certain, Norm's theory was a bacteria produced it. My theory has been it's produced by other algae, bigger algae like string algae, based on my own experiments and also that this type of behavior is common for organisms (allelochemicals). It's been seen in saltwater algae but freshwater algae hasn't been studied as far as I can tell. There is evidence coming from aquarist using string algae but they seem confused on why it works. Still, best theory I have.
What this all boils down to...
UV is 100% effective when done right, but watch ammonia. Often UV can be turned off after a week or month as string algae (macro algae) starts to grow. And you may never need to turn it on again. Then you'll want to know how to control string algae.
Trickle Towers and streams can be very effective because they give string algae a place to grow where they can get more sun, O2 and over come the defenses produced by the green water algae.
24/7 drip water changes can be effective. It basically flushes alway algae faster then they can reproduce and also gives string algae a better chance to grow.
Beyond that there are dozens, maybe hundreds of "cures". Magnets, barley straw, salt, bacteria, phosphate binders, etc... It's endless. And I'm pretty sure if any of them actually worked there wouldn't be hundreds of "cures".
That brings me to the point...be careful of the internet. I've seen more ponds filled in by people after trying dozens of "cures" promoted online and feeling like failures. #1 reason more people don't keep ponds are the pond "experts" promoting silliness online.
... i'm pretty sure the pond is getting too much sun, the sun hit the pond first thing in the mornings,,all the way through the day till approx 4pm and later as the days grow longer. over my previous pond we did have a sun sail , so today i put that up which covers a portion of the pond.
