1) Yes, high EC reduces the uptake of water. Actually, it reverses it when bad enough. If the EC of the solution is higher than that of the root, water will be drawn out. I got that from "Gardening Indoors with Soil and Hydroponics," by George F. Van Patten. Page 168. Also, this is why it is important to occasionally flush your medium for optimal growth. Salts build up in the medium making the EC too high and leading to dehydration even if your solution seems fine.
2) I don't recall the optimum temps for calcium, but was advised to shoot for 70-75F in general and I'd be "golden". I'm back in school now for biotech, so I will be sure to share anything relevant that I learn.
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