Last year the surface heater/deicer, and then the backup, on one of my koi ponds failed. Actually the second one developed a ground fault, but it's all the same since the circuit available there is on a GFCI. Under unusually heavy snow and very long periods of cold, this was the result:



Yes, there's a sixteen foot pond under there. All of my koi died, of course, probably from asphyxiation, four feet under the ice. No pictures of the carnage, as per usual.

This year, I did what everyone always told me to do, and dropped big airstones in. Three of them in one spot, because I'm paranoid. So far, so good:

That's interesting. How much ice is that likely to prevent? Obviously working so far. Nothing freezes here, but I came from eastern Wa., so am curious.

No idea. I've been told by various people that it won't freeze if I keep the bubbles going, but it does seem to me that there should be a limit to the temperatures at which this would work. The pond is sunk four feet in the ground, which is deep enough that most of it will never freeze here simply because of the ground warmth (frost line is 18" in the outer areas, probably only 12" where I'm at, and then, only in a particularly cold year--many years we only get a couple inches of frozen ground). I've placed the airstones in one corner, about three feet down, judging from the amount of airline that went in, hoping that it wouldn't stir up the sluggish fish or their warm spots. I don't know if the effect of bringing up ground-warmed water plays a role in keeping a hole in the ice.

We've seen temperatures in the low 20s since I put it in, but nothing sustained through the day under 25F or so. So no good data yet. I keep going out every couple days to see if the hole is still there in the early morning.

You have your air stones too low in the water at a 3' depth. I belong to a large pond forum, and most folks there recommend no more than a foot deep during the winter. You want as much agitation towards the surface as possible.

I have a small raised garden pond (425 gallons). I raised my air stones and still have my submersible filter running. I did add a Sunbubble to gain solar heat during the day. This past week we have had unseasonably cold temps with minus and single digits during the nights and teens and 20's during the day. We are predicted to have some single digit days later this week. So far, I haven't seen a sliver of ice, and I am hoping it stays that way. I would hate to have to stick my hand and arm 30" down in frigid water to pull that filter.

EDIT: Just went outside and this is the first day I have seen ice, and it is about 1" thick, but the area above the air stones and the area where I have the submersible filter discharge pointed towards the surface are ice free. I guess the constant real low temps this past few days are catching up. I did smack the sunbubble's vinyl siding on the 3 southern facing panels to clear them; the panels gets a coat of frosty ice at night due to the warmer water condensate that hits it. Clearing them allows greater sun penetration. Looks like we're going to have a sunny day, and I want to take advantage of any solar gain I can get.

I'm not sure why there'd be more agitation at the surface with them shallower. I've got them hooked to one of my large pumps with high psi and airflow. It is hard to raise the stones because of the steep sides of the pond, but if there's a good reason to I might be able to suspend them somehow.

Let me clarify. During the winter you're not getting any real aeration from the bubbles. One of the main reasons for the aerator in the winter is to keep a hole open in the ice. You have a better chance where the air has less resistance during the up flow. It betters your chance of the aerator keeping a hole open in the ice...more surface agitation.

Another reason for raising the air stones is that when set low, you pull the warmer water from the bottom and mix it with colder water nearer the surface. The idea is to keep as much warmth as you can where the fish hang out. Experiences of some of the seasoned vets on this other forum say the chances for a greater fish kill during winter months happens when the aerators are placed low in the water.

I'm going to have to disagree with the first point. Lots of pressure available means that the agitation is more vigorous when they are deeper. I have tested and verified this. More water is moved the deeper the stones get, and the surface agitation is visibly greater.

The second point is a good one, though, and was why I had placed them in a corner of the pond. I'll see if I can rig a way to get them farther up the steep side, once the ice thaws enough again for me to move them.

What you say about agitation does make sense to me, but what I wrote is the advice I've read many times on a pond forum I belong to. I'm not sure then why so many folks from that forum do it that way.

Some members there don't use their air stones at all, but instead use a "pond breather" during the winter months stating that it is far superior to using air stones. With a pond breather you don't have to worry about keeping a hole in the ice. The pond can freeze over completely, and a pond breather still releases the toxic gases.

drsfostersmith(DOT)com/product/prod_display.cfm?pcatid=18057

Interesting. Expensive, but I'll look into it.

Yeah, the old timers I know who use them, swear by them.

After some searching, this appears to be a single product, rather than a category of products. Reviews are mixed, with some saying it is ineffective or non-functional and others swearing by it. Examining the product and mode of action, my first impression is that it's a gimmick, and can't possibly do what it claims to. The positive testimonials make me wonder though. I'll check around locally and see if anyone around here has one that I can see, and can tell me about it.

Thanks for the lead.