yellowing tips of leaves?? help

hello....I have a flood and drain cabinet with 5 feminized plants. I am in the 6th week of veg and everything was going great. Looked at the plants this morning and three of the plants had 1-2 yellowing tips on them. It was time to do a nutrient change (using GH 3 part system), but I checked the PH before and it was at 7.0-7.2. Would this be the reason for the yellowing tips or is it something else I should be looking at? I wanted to put the plants into flower stage (12/12) this weekend, but was unsure if I should with the yellowing tips.

Any advise would be appreciated.

Thanks in advance

whats your ppm ?
crispi

If the pH was that high for awhile, it probably is the culprit, at least indirectly. Some nutrients are "locked out," (i.e. cannot be absorbed by the plant) at a pH in that range, such as Phosphorous and Calcium. Aim for a pH of 5.6-5.9 to avoid all nute lock-out issues.

It is a waste of effort to try to fix a suspected nutrient deficiency until you have your pH corrected and stable first. If the problem persists after 12-24 hours at the correct pH, then it is time to diagnose the nutrient deficiency and correct it.

You'll want to bring the pH back down gradually, so as not to shock your plants. Lower it by no more than .3 at a time, leaving it for several hours before lowering it some more.

The leaves that have yellowed at the tips will most likely stay that way, but if it gets worse after pH is corrected, then you still have a problem.

Once pH is good, you may want to trim off the yellowed tips so you can clearly see if more appears. If you prefer to preserve the leaf intact, take some good photos or measure the yellowed portion to guide you.

If chlorosis (yellowing) continues, look to see if it is on older leaves (this indicates a Macronutrient problem), or on newer growth (a Micronutrient problem).

Yellow tips on older leaves might be Calcium deficiency.
Yellow tips on new growth might be Sodium, Chlorine, or Copper deficiency.

Good luck!