Got a few problems with my plants not sure what it is though?

Hey guys my Swiss cheese and short Ryder from nirvana is growing good but I have a few problems I've encountered .

1. Very tips of the Swiss cheese is gone a little brown and there a few yellow spots on a couple of leaves.

2. Stem is sorta purpley? This any harm?

I'm running a 250w hps on 18/6 light just under 2 foot above them. I was thinking nute burn or heat stress? (it is quite hot as I haven't obtained a fan). Also I'm feeding both plants 1.25 ml of canna vega every 2 days ( the small amount is cause my soil is already rich in nutes) thanks

check this thread https://www.rollitup.org/general-marijuana-growing/420048-nute-burn-deficiency-guide-diagnosing.html

You reckon so? Even in fertilized soil and nutes? I don't think deficiancy. Thanks for the help though I had a look on that sticky and I'm sure it's over fertilzed