I don't figure this is a big problem, but I need to ask! I read on the forums that having a fan does two things, it speeds up growth of the plant because the more air, the more carbon stripped from the air. And secondly, that the stress of a breeze on seedlings forms stronger stems / branches. So I put a little fan near my plants, pointing away, on low. Am I being a scaredy cat? Do I want them rockin? Is a purple stem a strong stem?
just want a gentle breeze on them & yes they help strenghten up your stems,but do not put directly pointing too your ladies ,either have it oscilating or pointing off a wall so giving them that breeze they need as for purple stem thats either the strain or a heat issue, wont be a nute issue as only seedlings, so check the heat at night ,in fact check the heat regularly but i wouldnt worry no real issues to worry about hope this helps.
You might want to be a little more careful with small seedlings but as soon as the first set of true leaves comes out (not the cotyledon leaves) its safe to have them quivering. A purple stem is also quite normal for a seedling most grow out of it though.