What is this?

[Old Toker]

Week 8 of flowering....all sativas. DTW in 100% coco. 8x feedings daily. Good temp and RH control.
Noticed some yellow leaves and upped the EC to 1.3 from 1.2. Still relatively low. Saw this today.
Any ideas? I have one day to fix it....leaving town on Thursday won't be back until late Sunday night.

 

[troutman]

I think it's calcium issues.

https://www.icmag.com/ic/showthread.php?t=289088

 

[Old Toker]

Hard to tell. Seems as though every time someone reports a problem like this you never find out what the cause was.
Remedy is??? Flush with Ph 5.8 water and continue like before? Add Cal-Mag....add cal only? I'm using Tap at 134 PPM....takes quite a bit of down to bring the Ph down....

I think it's calcium issues.

https://www.icmag.com/ic/showthread.php?t=289088

 

[Old Toker]

Ok....for lack of better ideas/solutions and time....I decided to up my Ph in my rez to 6.3 and flush about a 1/2 a gal of feed through each of my plants. Supposedly plants uptake calcium better at a higher Ph. Normally I feed at 5.9-6.0....so we'll see if this helps.
Any other ideas/solutions? I have tomorrow night to try something else if anyone has a suggestion/comment.
Thanks!