Question
Hello, my name is Austin and it is currently winter where I live and it is very cold. I have never had any problems with my koi before but today I walked to my window and saw that my big white koi was belly up under the water. Upon further investigation of the pond I found a smaller one of my white koi, I believe from the same family, was also dead. As if it couldn't get any worse I noticed that two other of the white variety were on their sides but still alive. All of my other Koi, Lionheads, and goldfish seem to be doing fine and we have four air stones, two big two small, all running under the water of our pond. If one koi had died I wouldn't be too concered but when four of the same type do it is cause for question. Is there something I don't know about the white koi and why they are dying, or is there some problem I need to address? Please do reply to this, thank you very much!

Austin.

Answer
I've never heard of koi of certain colors being more likely to die.  I don't think they have died because they are white.  If they are related to one another, it could be that they have a gene that makes them less able to handle the cold or something.  How cold is it there?  Lionheads don't take the cold well so, if they are ok, I am not sure why other fish would not be.  Four air stones is a lot.  How big is your pond?  You may have too much aeration and water turnover.  You certainly want some but too much may disturb the fish or overcool them.  Did the dead koi show any injuries or symptoms?  You want to rule out predators who missed the fish.  It's not too likely this time of the year but our heron has been around this week in the snow (the ponds were netted).  Herons either eat the fish or leave holes in them.  

I'm not sure why your white koi have died but I don't think it's because they are white.  The only thing white koi are more suceptible too is sun burn.  I'm sorry I don't have a definitive answer for you.  As a precaution, check your water chemistry (pH, hardness, ammonia, nitrite, etc.) and maybe do a water change if the pond isn't completely frozen.

Good luck!