My 15-gallon tank was pea-green and I couldn't get a handle on the green algae bloom -- filter cleaning, partial water changes, blocking out light -- nothing helped. Enter this awesome little UV filter. It arrived on a Monday evening and I started it right up, running it in the tank along with my regular filter. The next day I noticed a difference. Each day the water was clearer, and on Friday it was no longer green at all, so I took the unit out to put it in another tank for a while. It worked miracles for the smaller tank, too. Now I have it back in the first tank, but I'm only running it about 3 hours per day, to save the bulb. My fish tank has literally never been clearer! Crystal clear water, and I can see all of my fish and the (too many) plants as well! 5 photos show 1) before the Green Killing Machine, 2) after 24 hours of Green Killing, 3) after 48 hours, 4) after the 3rd day and 5) 1 week later, with the Green Killing Machine running about 3 hours per day to maintain the amazing clarity.

SHORT VERSION:
IT WORKS. BUY IT!

LONG VERSION:
I had been waiting a couple weeks to write my review because I did not want to leave a bad review if it was actually going to work. My 55 gallon tank was in rough shape before buying this. I had a massive algae bloom in the past and had purchased another UV sterilizer (Sun brand I think...) and it worked, it cleaned the water, but after a couple of months, it stopped pumping water and was spraying out a black substance that was no doubt bad for my fish. When the algae got as bad as it did again, I wanted to buy another sterilizer but did not want to buy the same one I had previously. I took the chance and bought this little guy. My only regret was not buying the larger UV sterilizer for the extra $10. If you have a tank larger than 40 gal, I would recommend the larger watt sterilizer. Regardless...this one still worked!!

My tank went from not even being able to see the fish in it, to being crystal clear. My tank was in such bad shape that the attached was after 5 back-to-back water changes and it is STILL terribly cloudy. I popped this little guy in after I changed the water a billion times (my attempt to make it as easy as possible for the sterilizer) and I noticed a small change, but it was still cloudy. I was disappointed after 2 weeks because it wasn't crystal clear like it was last time I used a sterilizer (mind you, the tank was no where near as bad when I used the sterilizer originally). One morning I woke up and walked into the office and BAM....the water was transparent and my little fishies reappeared. I put the unit in my tank on January 22, 2018 and i noticed it was clean on March 7, 2018, although it had been clear for at least 1-2 weeks and I never really put 2 and 2 together and said "oh hey! The sterilizer worked!". Also, I did not do ANY water changes during this time, but did change the water on January 22, prior to putting the unit in.

The set up of this sterilizer is 1,000 times better than the Sun brand one I had purchased. Easier to clean and the filter sponge is much better in this one (the other was inside the unit and would constantly get clogged and stop all water output. I eventually removed the sponge after fighting with the unit to open it and it worked again but the motor gave up after only a short period of time). This one has the sponge on the exterior so you can clean it out easily. It also isn't as forceful as the other sterilizer which my fish HATED because it was such a strong output (when it worked). This little sucker cleaned the whole tank and it is now gorgeous water again. It did take a little longer than I was expecting so just BE PATIENT. It will work, it just needs some time to filter through all the water. A+++++ from me!

I have attached the progress of the sterilizer from Jan. 22 until tonight, March 9. Happy fishing!!

Unbelievable results!!! Battled algae for 2 months in my 10 gallon tank. Tried everything from drops, filter packs, tablets and nothing worked. My tank was a consistent green and I could barely see the fish. Then I purchased this green killing machine! Did a 25% water change, installed this in the tank and plugged it in. Next day it became a light green and in 49 hours was crystal clear! I put it on a timer so it now runs 4 hours at night and my tank has been clear for the last 2 months!!! Highly recommend and see pics!!!

For a while my fish tank was looking good. No algae, nothing. Did a regular maintenance partial water change. Then it all went downhill. Water became more and more cloudy. Then it just turned straight green. Fish were still alive...I think... I saw something swimming in there. So decided to just go ahead and did a complete water change. Pulled out all the decorations and gravel and gave them a good cleaning. (No soap was used btw). Put everything back, filled tank up. The very next day, water was green and cloudy. Next day after, it looked as if I did nothing at all. What...the...heck! So I went online to do a little research to see how I can control this out of control algae problem. I read additives didn't really work. So I was thinking I was doomed to a green tank forever. Then I discovered this gadget. Reviews were rave talking how waters were cleared within a week, tanks restored to tropical paradises and such. I'm thinking it couldn't really be that easy...can it? Eh why not, let's give it a try. I did no water change whatsoever. Just unpacked it, installed it and let it go to work. Question is, did it work? Check out my pictures. They are taken every 3 days. A week later, call me impressed. It really was that easy. I'll still do a partial water change just to help it along but the fact that it did that good a job without it...I'd say this was 40 some bucks very well spent.

My 40 gallon tank was more cloudy than green, but it was algae (from my new light). I put the GKM on my tank on Saturday. Sunday and Monday, it still looked the same. On Tuesday, the magic started happening. Today, I'd say my tank was 90% clear. I can see straight through it. By Saturday, the tank should be crystal clear. I still want to get the 24 watt GKM. What a great product.
2/14/17 update: the last picture is proof. The 10th day, crystal clear, even after a weekend of planting new plants and adding Eco Complete substrate. Incredible.
5/17/17: I noticed that the aquarium walls were turning green again. I noticed that no water was coming out of the pump. I'm very disappointed. I thought it would last longer than three months.