Welcome, Redblazer. I think IV lights should not freeze. If that's the case, you should remove it and put it indoors for winter. If you have it in-line, then hopefully you can simply reconnect that line to the other side for the winter, if it's a "running" line.
I learned that it's best to keep everything up and running in the winter, as long as possible and as soon as possible in the spring, if the weather allows it. I live in south central IL, Zone 6a. We get down to the teens and sometimes below zero, but not for long. Last winter was another mild winter, only had a few times where the ponds froze. I set up an air bubbler just in front of my skimmer in koi pond, water bubbler (fountain pump just under the water surface) in front of the skimmer in the goldfish pond. That way, it helps keep the water from freezing too deep at the skimmer opening. I leave the pumps running in the skimmers all winter. One skimmer pump runs the water to the koi bog, the other to the top of the stream. The idea is running water will not freeze. The only problem comes about if your pump gets clogged and quits. Then it's a matter of unplugging that pump, and waiting out the cold spell.
When the water freezes, I put my floating heater on one pond at a time, melt a hole above where the bubbler is, and then turn on the bubbler. Last year, didn't even need to leave the bubbler on all the time. If it's only keeping a 2-3' hole open, I leave it on. If the whole pond thaws out, I shut it off.
Couple of things I learned last winter: Don't turn on an air bubbler when the pond is completely frozen over! It created an air pocket that kept getting larger and larger, eventually cracking the ice. I shut off the air before this happened, and put the floating heater on top to open an hole. Don't want ice cracking over the ponds, and don't want to chop the ice to break it either. Dangerous for the goldfish and koi. VERY loud sounds in the water.
I also moved all water lines that were outside the pond liner to inside where possible, so if there is any break in the line during the winter, I won't almost empty a pond again. Thank goodness someone said to put bottom of pond pump up on a shelf (I used a milk crate), or I would have had frozen dead fish that cold January evening! All was well, though, lost no fish. Lesson learned on water lines.
Good luck with winterizing your pond! As long as the pond is deep enough, your fish will be happy when spring rolls around and water warms up again.
