GreenFree UV Clarifiers

5-Watt GreenFree UV Clarifiers
  • 5-Watt GreenFree UV Clarifiers
  • Tetra Pond 9-watt UV clarifier
  • 18-Watt GreenFree UV Clarifiers
  • 36-Watt GreenFree UV Clarifiers
Product No. 19523
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Making how to get rid of pond algae for good possible!

GreenFree UV Clarifiers work to keep your pond clean, clear, and free of green algae. These dependable clarifiers use ultraviolet light to destroy suspended green algae. As algae are pumped into the Clarifier they are exposed to Ultra-Violet light that destroys the reproductive ability of single celled algae. The dead algae is then pumped out of the Clarifier where it clumps and is removed by your tank’s filtration system. Tetra UV Clarifiers can typically remove heavy algae blooms within five days and keep your pond algae-free long term. GreenFree UV Clarifiers are easy to conceal, durable, install in minutes, and feature a 3-year limited warranty. UL listed. 15 foot power cord.

This product comes in the following sizes:
5 Watt for ponds up to 660 Gallons
9 Watt for ponds up to 1800 Gallons
18 Watt for ponds up to 4400 Gallons
36 Watt for ponds up to 8800 Gallons
GreenFree UV Clarifiers is rated 3.8 out of 5 by 12.
Rated 5 out of 5 by from Great product This is my third year with the Tetra UV. Once I learned to control the speed of water through the device I can't be more happy. No green water! It is so nice to enjoy clear water, knowing both my fish and I are happier. Tetra products have always given me better service than other brands and customer service has always been great for me.
Date published: 2017-07-20
Rated 5 out of 5 by from Works as promised Had very green water in my small pond. Bought the Greenfree UV and a week later the water is clear.
Date published: 2017-06-10
Rated 4 out of 5 by from UVC-18 Bought a UVC-18 for our 2,839 gallon pond about a month ago. Seems to be working fine; cleared up our water in about three days and wish I had done so a year ago. Nice to be able to see the fish and bottom of pond. Only thing it took a bit of working on our part to find the right hose and connect UV filter into our plumbing for the pond.
Date published: 2017-05-31
Rated 4 out of 5 by from Clear Pond I bought a UV 01K37 or Item #19520 and the end broke - I emailed Tetra and received a new UV last year or summer before. This year we've bought 2 new replacement bulbs for our unit and neather bulb would light up. We just found out the bulb connection part is bad, we exchanged with the old UV unit and bulb is lite. Should the bulb connection end go bad that quickly?
Date published: 2017-05-07
Rated 1 out of 5 by from terrible warranty bought this last year and the insert broke off and emptied my pond and killed my 15 year old fish. I wrote tetra and said I needed my receipt which I didn't have so I spent all that darn money for nothing and lost my fish on top of it. That thick plastic thing that goes into unit that attached to hose to filter broke in half. I had bought at least 3 of these and refuse to buy another one just to have it broken and never able to get it fixed.
Date published: 2017-04-07
Rated 1 out of 5 by from UVC-36 greenfree ultrviolet clarifier not good Just received our second ultraviolet clarifier and found out the changes made from the 2009 model we have been using created some problems that the 800 number people we called for advise at tetra cold not even give a response for a possible solution. The new unit changed the maximum diameter size for intake and exit hoses from 1 5/8" to 1 1/4". Spent 3 hours going to plumbing supply houses, hardware stores and big box stores to try to find a way to adapt our 1/5/8" hoses we have on our pond to the 1 1/4" maximum now provided on the newer model. Came home and called the 800 number for advise and they said "things change" and that was it. I would think they would have worked out a solution to prevent having to change out our supply and exit hoses for both our ponds but no only the response "things change". Not an acceptable response for a help line.
Date published: 2016-08-17
Rated 5 out of 5 by from works great We have had our pond since 2002 and this works great except when someone left it out all winter (Bflo NY) and it cracked. So we are replacing it with another UCV 18 and our fish will enjoy another wonderful summer. I do also use the barley bales since our pond does get full sun for a large part of the day. Just wish there was a way to stop the hair algae from growing
Date published: 2016-04-30
Rated 5 out of 5 by from Great Product and Great Service I bought this product because the filter I had with the UV light built in failed on me. The filter still works great its just the light unit no longer works, after only 3 years. I didn't want to get rid of the filter so I purchased the UVC-18 Clarifier. I had only just set it up and realized there was no Purple Light indicating that the bulb was working. I waited till evening to check incase it was a dim display or something. Still no light. The next day I unhooked it checked to make sure it was all put together and the bulb was properly installed, it was. I called the 1-800 help line and got to speak to a Tech. It appears the safety stitch was not turning the light on. The Tech told me how to fix it and it worked. Now it is working great. Hopefully it will only take a few days to get my Pond back to crystal clear status. I enjoy the sturdy construction of this unit. It feels like it will last and no cheap plastic at all. Only time will tell. I have a few other products from Tetra and all are working great. I have a Tetra pump it is still going strong even after 5 years!
Date published: 2016-04-21
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I live in California. The temperatures here get down into the low 30's at it's coldest so my water never freezes. I leave my filters on all year. Do I need to pull the unit when the temperatures drop?

Asked by: Nonno
Yes, you should as freezing could cause the glass internal sleeve to crack, and water to damage the ballast. Also, at those temps you should not get a lot of algae. BREX
Answered by: BREX
Date published: 2017-11-03

What is the minimum flow for the 9 watt unit? Is 900 is max or is that the optimum flow? Also, the unit should not be submerged, but is it safe in the rain? I am running the unit separate from the main filtration which is running higher. pond is 1600 gals

Asked by: Nonno
The flow rate for the 9 watt is up to 1800 gallons per hour. Optimum flow is 800 gph since your pond is 1600 gallons. You want to move 50% of the total pond volume through the light every hour. It's perfectly fine in the rain. BREX
Answered by: BREX
Date published: 2017-10-30

Does this unit have an indicator light to see if the ultraviolet light needs to be replaced?

Asked by: DonD1
Yes, there is a small, oval shaped opaque window. Check it in total darkness. BREX
Answered by: BREX
Date published: 2017-10-25

How do I go about getting a replacement part for my uv light. The item # is 19521. It is a 19.5w and the fitting where I attach the hose from the pump broke off

Asked by: RLodo
We don't make a 19.5 watt, so if it is ours, it would need to be an 18 watt. BREX
Answered by: BREX
Date published: 2017-10-16

I cannot find the viewing window on unit number l16788. Can u tell me location

Asked by: Sam18238
It is a small oval opaque plastic area near the end with the screw on cap. BREX
Answered by: BREX
Date published: 2017-09-25

I need a direct (or close) replacement for my TetraPond K20.  It's been in use every year for many years and now I'm afraid the seal is broken between the glass tube and the plastic collar.  I have UV lights so obviously I'd want a housing that they fit.

Asked by: David Winter
K20 is a lot code. That tells me it is 19 years old! I don't know what size you own, but we have changed the design a couple of times in 19 years. You would need to purchase a new light. Adapters have changed a bit too, so you might want to call 1-800-526-0650 so we can help determine which one you should buy. BREX
Answered by: BREX
Date published: 2017-09-21

Will your Tetra Pond 5 watt GreenFree UV Clarifier work on a small pond using around a 3gph pump

Asked by: Spazz
3gph won't even move water through it! You would need at least 200 gph. I cannot imagine moving so little water, so please call in to discuss this further, and see if we can provide some useful advice. 1-800-526-0650. BREX
Answered by: BREX
Date published: 2017-09-15

What size uv clarifler do I need for a 200 gallon pond

Asked by: Hotdogfin
We would recommend the UVC-5watt which is for ponds up to 660 gallons, with a pump of no more than 300 gph. BREX
Answered by: BREX
Date published: 2017-09-13
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GreenFree UV Clarifier Guide


Pond Size

Tubing Adapters Included

Max Flow


Up to 660 gallons

3/4", 1", 1 1/4" ID

330 GPH


Up to 1800 gallons

3/4", 1", 1 1/4" ID

900 GPH


Up to 4400 gallons

3/4", 1", 1 1/4" ID

2200 GPH


Up to 8800 gallons

3/4", 1", 1 1/4" ID

4400 GPH