Quote:
Originally Posted by
koibooi 
When I build my first 30 ton pond about three years ago I installed 3 x 50watt UV lights. Over time I changed the UV tubes about once a year and have never had any green water problems even though the pond is in full sun. Water temperature where I live in SA seldom goes below 18 Celsius but can get to 29 Celsius.
From the beginning of October this year I started having green water problems. I replaced the UV tubes and it still did not go away. It got so bad that I did an 80% water change but a few days later it was back. I tried all kinds of pond treatments but it would clear up for a day and then be back again.
At this time I also commissioned an 8 ton quarantine pond. I did not connect the UV straight away as the electrics were still being finished. About 4 weeks after filling, the water also started going green. Once the electrics were completed the 15 watt UV went on and 2 days late the Q-pond water was clear.
This caused me to re-look at the main pond UV's. First thing I noticed was that the tube was not burning as bright as the Q-pond. Upon opening the ballast, I saw that water entered the controls and rusted the small transformer. Checking the other two UV's revealed the same.
I bought 3 new 55 watt UV units and installed them and two days later all my green water problems were gone. Never again will I question the effectiveness of something as simple as a UV. So the lesson is that should your water be turning green when your pond comes out of its winter sleep, make sure that your UV lights are burning bright.