Yellow Leaf tips... Please help!

Plant seems healthy and is growing but all new leaves have yellow tips!

Medium: Low nute "professional grade" soil (.09, .04, .06) mixed with sand and perlite - 2:1:1.
Lighting: All CFL - 1-125w (6500k), 2-42w (6500k) & 2-42w (2700k) = 293w CFL total. About 3-4" from plant tops.
PH: Soil - 6.8. Water - 6.8 (tap water - adjusted with apple cider vinegar and left out for 48 hours before applying to plants)
Temps- 77-84. Thermometer with remote sensor positioned a little higher than plant top level.
Nutes: None

Note: Bottom leaves were salt burned. It was flushed yesterday and all new growth has yellow tips - only yellow tips. All other growth is green besides the tips. Should the flush take care of this? I'm not sure what else I could do. On paper everything seems to be right.

One day is not enough time to really tell. How much water did you use to flush?
BTW do the pH adjustment immediately before using the liquid. It may actually drift overnight.

I honestly can't say if this is an issue or not but I personally would try losing the "apple cider vinegar" and go with true ph up/down from a hydro store. ;)

What's low grade professional soil? Never mind...I'm sure Stinkster knows.

I told him to use the cider vinegar instead of the pool chems as a stopgap measure until he gets 'real' plant chems. I'd say 'low grade professional soil' would be equivalent to a knockoff store brand promix type bagged medium with peat, lime, and perlite.