Brown Spots on Leaves...PH or Mag Def?

Hi Guys;
Currently i have a grow going in the CFL section entitled PLL SERVER GROW. I am noticing some issues with my girls and I want to see someone could help me determine whats going on.

Details:
week 5 of flowering
Cfl Grow
avg temp 85
soil - Dr Green Earth Organics
AN Sensi Bloom A&B - 5ml per gal
AN Big Bud - 5ml per gal
AN Bud Candy - 5ml per gal
I use un-ph'd Reverse Osmosis water from the store...(think this might be the problem)
Side note: I noticed my soil has dusty white appearance to it...may be from the salt? I have flushed twice in the past 2 weeks with un-ph'd water but it doesn't seem to be helping much..


They have been growing rapidly and look healthy except for those brown spots that just started appearing.

Calcium and Mag deficiency. Brown spots from calcium and the light green fading spots are from mag.
Book mark this guide. It is the best I found online. http://www.icmag.com/ic/showthread.php?t=11688

I agree with hempstead,tx.

But is this deficiency caused by lockout due to pH, or is there a lack of calcium/magnesium in the grow medium?

That is the question.

Hard to tell from the pics but it doesn't look like pH. Everytime I had a pH problem the plants leaves would kinda warp and twist looking almost deformed. That second pic looks like a little burn because of the tips of the leaves but nothing serious. Some of my plants had that problem after a heavy feeding but never went beyond the tips. Look at your plants and then look at that guide I posted and see if any of it looks familiar. Good luck.

The deficiency is caused by the fact that you are now 5 weeks into flower and they really need extra Mg during the first, say, three weeks of flowering. So now you are a little deficient. Store water usually has about 50 ppm dissolved minerals in it and that's okay for vegging but you need a little extra in early flower. Store bought pH is usually around 6.8-7.0 which we like, but not so good for plant mineral absorption.

Here's the chart:

View attachment 1688867

You can see where both calcium and magnesium get locked out at lower pH levels in soil, at 5 weeks flowering I will have already adjusted my water to 6.5 whereas in veg the water is adjusted to 6.2.

I think you have to look at your pH first, then decide whether to supplement with calmag or adjust pH.

I could be wrong.

Thank you so much guys. So the first thing I am going to do is PH my water and see if the cal mag def improves. If not I will get some cal/mag nutes to help them out

Thanks for the bookmark hempstead it was great read!

Based on WBD's chart for soil it seems that the higher the PH the better the absorption is for Cal & Mag....do you think it could be possible that I may be to low on PH rather than two high? Thus causing the nute lock out?

BMWEATER said:

UPDATE:

So I finally figured out what my problem was-LOW PH. Bought a General Hydro PH Kit and tested my water its PH was 7.0. Then I tested it after I added all my nutes, it had dropped to 5.0!! So that's why I was getting lock out.

I feed them with 6.5 PH'D water and checked the run off...it was a light 6.5. So I hope this will fix it all! Thank you so much for all the help!

Click to expand...

Good job, been there done that. Except I had the pH tester, I just ASSUMED that my water was a certain pH. Magnesium def. seems to show up really quick when pH is out of range because my plants went downhill fast! It cost me all my big fan leaves, many of the medium sized ones, and an extra 2-3 weeks of flower time. I hope you are not as far gone as I was...

P.S. be careful with jerking your pH up that high again suddenly, the plant will go into shock with major fluctuations of pH. How low the pH of the soil actually got is the whole question... how man times did you water with 5.0 water? Be careful...

BMWEATER said:

Thank you so much guys. So the first thing I am going to do is PH my water and see if the cal mag def improves. If not I will get some cal/mag nutes to help them out

Click to expand...

This was the right approach. Throwing nutes/supplements at a problem (as unfortunately suggested by others) will be futile if your pH is fucked. Also, if you're feeding with quality product that should be all your plant ever needs, so any deficient-looking leaf problems could almost certainly be pH-related and not an ACTUAL deficiency.