I don't know specifically about the CalPump sterilizer, but they all work about the same. The CalPump sterilizer you are looking at is also advertised at webbsonline.com for $210, shipping included. Webbsonline is a long-established, solid vendor. Other options include a UV40-watt Pondmaster sterilizer offered at AZponds.com, for $185 (shipping included). I personally operate a Tetra 18-Watt UV2 sterilizer 24 hours a day and it works perfectly. AZponds offers the 36-watt version of the Tetra sterilizer (model UV3) for $230. The Tetra UV3 comes with a spare 36-watt replacement bulb, and they are expensive. Personally, if I needed a 36-watt unit, that's the one I'd get based on my experience with Tetra. If you can go with a slightly smaller unit, AZponds offers the CalPump 18-watt version, which is rated for a 2,000 gallon pond, for $75 on close-out, shipping included. Hope this helps.

>>Send back, why not? Thanks for your response. Because the old model has a better internal reflector, and if I send it back, they will probably send me the newer model. The reflector on my newer model has already failed. So it might be nice to have the older model, with the good reflector and just change the ballast. Just wondering if replacing the ballast is a reasonable option.

For green water a UV should clear water in 3-5 days imo. The change can seem sudden if you wake up in the morning and can see the pond bottom. What really happens is the algae is killed pretty fast, maybe 8 hours. But it takes some time for the green to decompose out of the cells leaving an almost translucent cell behind which are also smaller. Some clump and sink. What UV do you have? 10-14 days bothers me. Clarifier is not a precise term, so sellers can get creative. Most manufacturers provide info on flow rates for both sterilizer and clarifier. I always use the sterilizer flow rate when comparing units, apples to apples. Taking 10-14 days could mean a very weak UV for the advertised flow rating. In a bright green pond single algae are that, single cells, easy to get a high UV dose. After a year many cells will have clumped together into what is called "colonies". They do this as protection from the sun's UV. It also gives them some protection from UV filters as it takes many more trips thru the filter. Add a bunch of other suspended particles, plus a weak UV, could be issues. Diggery is right, not enough info to really know anything. A red flag to me is a pond that hasn't been clear in a year may appear green but be a combination of things. After cleaning different ponds for awhile you're able to tell a lot from just seeing the water.

I have 25 watt on 1500 gallon; it is sufficient. You may need to put it on a bypass with added valves to slow the water flow enough to make it most effective. On my setup part of the water is diverted to the UV from the filter before it flows back into the pond. The slower water spends more time being exposed to the UV light, making it more effective. I adjust the flow via ball valves. Look at the manufacturer's information to determine the most effective flow, and a flow meter is invaluable for determining what your flow really is. Just as a side note, 12 koi in 1400 gallon is a lot. Yes they are small now, but they will grow quickly to a size you could never imagine. I have 7 koi in 1500 and the filter is just barely keeping up with them. I'm adding another filter and foam fractionator soon. Koi are dirty fish that produce a lot of waste. Just keep that it mind--it's not a problem now but it will be in the near future.