I don't hate the experts @Dave 54 - I just don't necessarily always believe what they say. I have that kind of personality - I question and test just about everything I hear or read. As I mentioned in another thread, there are lots and lots and LOTS of examples of times that the "experts" have been proven wrong. So I take what "they" say with a grain of salt.
I do, however, always believe what I can observe with my own eyes. I have seen dozens of ponds that are only 2 feet deep in our climate stocked with koi that thrive in our winter temps. How do you argue with what you can see?
The OP also mentioned his fish had survived in his pond for 15 years. Two things changed in those years - his fish got bigger and this year was colder. You assumed it was the colder weather. I assume it's the size of the fish - he finally reached the tipping point. Is cold weather stressful for fish? I'm sure it is. But moving fish from outdoors to indoors is said to be stressful, too, and yet lots of ponders do it as a routine practice. In a perfect world our fish would experience no stress. In the real world, we can only minimize it as much as possible.
As for deeper being better - we met a man in a pond store who was rebuilding his pond. His original pond was 4x4 and nearly six feet deep. Time after time his fish died. He determined from his experience that surface area is also an important factor in allowing your pond to off-gas. (He was forced to rebuild when the sidewalls started collapsing - digging a hole that deep isn't necessarily the safest thing to do.)
You know I find it strange why we here in the UK with the deeper koi ponds seem not to get these problems and you guys still dont get it our fish survive yours seem to suffer..why ?
Time after time I've talked on about being prepared for winter, I do it every year not only to remind us but for the newbie what the pitfalls can be etc.
Lisa i dont asume the OP's winters have grown harder I know so from the very reports that come in not just from the OP but from others.
Plus what we see on the news and read on the net or read in the papers l so Yes I will call into question the depth of a persons pond its only logical that I do .
I do have some idea of the US climate and that of certain parts of the world visited by myself over the years and I've identified as a major problem of your repearedly being visited by the polar vortex and the problems metion by both Meyer and your good self
Lisa Slick and I follow a set of rules set out buy the BKKS and our local setion mine would be Plymouth and Slicks I think North Yorkshire we lean our ponds and filters as prescribed we get long hard winters perhap not as hard as yours but they are long and hard yet we seem to get no losses and Val and I havent since we moved outside .
In my section we have the former head of the BKKS Health standards committee , He's my mentor I've learned alott from him and one of those things was how to keep koi alive throughout winter.
Each year we do our set routines and by late Autumn we are ready for winter covers and all and we have no problems neither do we see problems in the spring
@Andy41 has seen the quality we keep our koi at he visited last year if you recall .
Now this winter may only be our 6th of the 28 years weve been keeping but we took onboard what was being said to us , weve had no losses of koi , weve even saw temperatures of -15c with a hard snow (and that was under aa bubble wrapped frame pre polycarbonate roofing sheet) this was on our very first year outside ,though thanfully this year was only -10c it is stilll very cold for koi carp yet we allow no ice we have a temperature under the covers of 7c unheated.
What works for us guys should work for you so why not try digging those ponds that bit deeper live by rules set out by others even if you dont join the club.
If these vortex's are going to keep on year on year your going to have to address this at some level or other.
It's only logical you do this , so please forgive me for being the caring sort
Dave
