My 1800 gallon pond has biofalls and I seed the pond with beneficial bacteria often but when the air temps are above 90F, the clouds of green single-cell algae thrive, and water clarity suffers (ie visibility drops to one inch).

So added this 900 with UV lamp as a additonal filter and aerator. Worked great. Within one week, pond clarity is crystal clear and visibility is all the way to the bottom. Was easy to set up and I like that the pump/filter is totally submersible in the pond (expect for the rain shower snorkel). In addition to filtraron, adds aeration to pond as well. The LED light at night is a nice feature. I wish there was as easy indicator to quickly show that the UV light is functioning. It is possible to check such, but takes a small amount of effort. Otherwise, it worked great for me and I highly recommend.

See before and after photos. Suspended single cell green algae inn first photo. Can see to the bottom in second photo.

Just ordered replacement UV bulbs for nexts years to come.

Got the 600 because we wanted the fountain/waterfall feature and more cleaning power. In 5 days you can see how it cleared the 100 gallon pond, no filter change yet so we think the UV light is doing its thing. We are beyond happy with this purchase. The night light is a plus and it pumps a strong stream to the waterfall feature which can be adjusted. The only odd thing is that it kind of wants to float when first submerged but it eventually stayed down. We are happy overall and hope it keeps working for many years. Do be patient with it if your pond is large, I was getting discouraged by day 2 but it just needed time.

See the difference for yourself. 300 gallon pond. Algae started growing faster than usual. The first pix show after one hour. The second pix is after 7 days.
The first pix had a separate pump for the waterfall. The second is using the UV filter pump only without the fountain. It doesn't have the pressure of the original setup. However, there is less water turbulence so floating water plant, like salvinia and azolla, will grow better.

Cleared up my pond in a couple of days. works great. The only this that would be nice is to be able to turn the light off if you wanted to. It is either on all the time or on when it is dark, but not a big problem.
Have to clean it regularly but it is easy to clean.

I purchased this unit in the fall of 2022 and it has run continuously since then. As a filter and water clarifier it is working great. On the T-piece there are two control flow knobs and I need to replace one of them, but I'm having a hard time finding replacement parts. The light started to strobe on and off recently, even after I tried to correct it, but I'll keep fiddling with it.