Hey there. In zone 6a you shouldn't have a problem with running the pump/bio filter all winter. I'm in zone 5 and mine runs all winter since I got up the courage to try it. But, and it is a big but, a lot depends on the size and depth of the pond, the size of the pump and how cold it gets.

One of the smaller ponds I built that was shallow (18 inches) and only held 150 gallons froze so badly that the tubing froze closed and almost wrecked the pump and since the water was pumped onto the top of the ice and couldn't get back under it, there was no water left under the ice to pump which wasn't good for the pump either.

At the same time a larger pond, 1000 gallons, 3 ft deep with water running through a large Skippy filter made lots of ice but the falling water created a tube where the water was moving too quickly to freeze. Rather pretty. The surface area there is about 10x10. I also run a bubbler 24/7. No other deicer has been necessary. The pump volume is about 1570 gallons per hour.

If you have 25 fish your pond is probably at least 1000 gallons so if it is not extremely shallow and your pump is adequate, you probably won't have a problem. If you have to choose between a pump and a bubbler take out the pump. So long as the water continues to be aerated the fishes will be fine.

Algae does not grow in really cold water so you could take out the UV. Don't leave it in if it isn't running or the tube could shatter from the cold.

The muddy water on the bottom is probably mulm (poop and organic debris settling to the lowest level. If there isn't a lot and your water is otherwise clear and healthy (test the water)you can leave if for now. Vacuum it up when the weather is warmer or move the input tube closer to it now.

Is there some reason you can't allow the water to drain over the side or out an overflow tube? In most cases, unless you have a real gusher the water level should not get so high to cause a lot of overflow. It seems a lot of trouble to lower the water level before a rain. Usually there has been enough evaporation to drop the level and the rain just tops it off. The only reason I can imagine is if the pond is not above the surrounding ground level. Then you might have a problem with runoff going into the pond and that is something you need to avoid in the first place.

another image

This post was edited by Ryannair on Fri, Dec 28, 12 at 13:10

Ryan, I haven't a clue as to the set up on your bio filter and UV. The UV I have is separate from the (Skippy) filter. I hope someone familiar with yours will show up soon. My first UV was left unplugged outside and the bulb shattered in the cold.

In natural ponds it is common for the water to get cloudy during rain. An artificial pond with a layer of mulm or organic material could do the same.

In your second photo it seems you don't have a liner all the way up to ground level but that could be a mistaken impression. If the liner is not above ground level, then you could easily be getting runoff. A pond edge must be higher than the surrounding ground. How about some additional info?

To see if your filter is doing the job, collect some water from the waterfall and let it sit for an hour. If the water has a lot stuff settle out the filter may need cleaning or you may need more filtration.

Do the fishies dig in the planters? Do you have critters that visit? It's really hard to be certain about anything without more info.

An overflow is just a place or device that allows excess water to drain away from the pond. It can be a spot where the liner edge is slightly lower or it might be a piece of pipe that goes through the side. It just needs to drain away from the pond far enough that it doesn't weaken the sidewall.

Do you do any water changes? What kind of liner do you have?