Smoking? Is it possible for something to smoke underwater? I would think that if it were releasing that, you would see some kind of reaction going on on the surface.
If it was actual smoke, your baby cories don't have anything to do with it. Either your tank is WAY too hot (to the point your fish would have been dead ages ago), or you have a case of spontaneous combustion going on!
Personally, I think what you saw wasn't a gas or vapor. I think you saw a blob of white slime. That's the best I can describe it, and it has occurred in my tank, and the tanks of many other members on here. These blobs range in size, and sometimes float around the tank, but usually are seen clinging to plants. At first glance, they do look like little whifs of white smoke because of how they move in the water. I have read that they are decayed plant matter, and you can easily scoop them out. Do you have live plants? If so, that's probably it. I doubt they are dangerous at all, but if left in the tank, along with any other blobs that may occur, I would say your nitrates might start rising.
HTH!
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