I don't do perlite or hydro whatsoever, granted, but am I the only one who thinks either the plant actually is afflicted with a deficiency or it is something else? 72 ppm isn't a lot at all... my local tap water comes out of the faucet a bit higher than that, and it could barely be considered 'hard water'. It's been two weeks and perlite has virtually nothing for plant available nutrients of any kind... Soil may sustain a seedling for several weeks, and a good sphagnum or coir based straight potting mix for a couple weeks perhaps. Just perlite, on the other hand, no minerals to speak of you need to start fertilizing lightly earlier.
Correct me if I am wrong, but even a 2 week old seedling should be able to tolerate (if not require) 250 ppm at least, given nothing in the growth media.
