I'm liking that fan leaf too
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If you are using a 1000w hps it will give about 3' or maybe a little less throw of useful light. So there is not much point ending up with a canopy deeper than 3 feet. Of course you can always train the plants out sideways.
Bear in mind the plant will stretch at the onset of flowering. I think purp urk is indica dominant so they might not stretch that much. Here's a link to an lst thread.
http://www.yahooka.com/forum/growing...-training.html
Epsom salts- magnesium sulphate. About 1 tsp per gallon. The plants look healthy enough in the pics as far as I can see but imo would do no harm to give them a light dose now.
If you're going to top up the soil I'd use whatever soil you've been using already, just for the sake of consistency.