Fresh cider is sucking water through airlock

[warminghut]

It's official: I'm in panic mode.

I have eight single gallon batches fermenting for about a month. Through various experiments I came to a plan for a 5 gallon batch that I expected to be the good stuff. 125lbs pressed this past Sunday. Was going to pitch the yeast tomorrow, without campden. Woke up today to see 2 or 3 tiny spots of mold on the surface of the juice and noticed that the airlock was low on water. I, in an attempt to save a batch that has already cost a lot of sweat (picked most apples myself) and money, dosed the whole thing with campden tablets this afternoon, and refilled the airlock. Now, the airlock is low again.

What's happening? Why is it sucking water back through? What did I do wrong? Can I do anything to save it?

 

[gratus fermentatio]

Usually when you get "suckback," it's due to temperature differential, but even a change in weather, specifically the barometric pressure, can cause it. Had any storms in your area lately? It all boils down to lower pressure inside the carbouy than outside. There are a few things you can do to prevent it, like switching from a 3 piece airlock to an "S" shaped airlock, or you could use a blowoff tube.

Another thing you can do is to use alcohol (cheap vodka works well) or even Starsan in your airlocks instead of water. This won't prevent suckback, but it will prevent anything nasty getting into your cider. Now as for what to do with your current batch...
If there really is mold on the surface, I think you did good when you hit it with campden, but you might want to try racking from under the mold if you can. If you can remove the mold from the cider, or more accurately, remove the cider from the mold, you might be able to nip it in the bud as it were. You might want to hit it with campden after you rack, just to be on the safe side.
Hope this info helps. Regards, GF.