I can't seem to find out what this is. 2 plants have these spots. One seems to have gotten over it and has them only on a couple of lower leaves. This one has spots on newer growth as well as older. I can't find any bugs and the spots seem to originate on the top side of the leaf. Thanks in advance for any ideas. I couldn't find anything in faq's that addresses this.

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Also, the spots seem to start right on the veins, then get bigger. Eventually, the leaf turns yellow and gets crispy. Please help.

Hey Pappy,

I'm just a rookie, but my first thought would be what the Ph and PPM's are (if hydro).

Could be some kind of mag def. issue, or maybe a nute burn?

Beatshelloutame! But, I know someone here will have the knowledge you need to get this fixed and your plant back to Happy Days!

ISO

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well i can't really tell by the blurry pic but dark dots i only know from fungus... but it could be all wrong and be some fertilizer caused burn too... have a look at this table Grow Marijuana FAQ, Cannabis cultivation - marijuana growing tips & photos and maybe get some better pic of the problem - maybe your cam has a macro function, try a shot with this.

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Keep the gun oiled and the thumb green!

Thanks green,
I think it needs some Mg. Will take care of it in the morning. Again, thanks.

Okay I need you to help me out with some more info here.

Are the leaves still nice and green other then the spots?

What is the humidity level?

Do you have air circulating in your grow area?

Do you exhaust your old or stale air out or the room?

Do you ph test your water?

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The leaves get yellow after a few spots show up. They're green when the first ones show. Spots get bigger and leaves yellow.
Humidity varies between 30 - 38%
Lots of air movement.
Grow area is 4' x 12', which is within a 14' x 18' room.
Grow area is exhausted with 6" duct and fan, into the 14 x 18 room.
I enter the room many times a day.
The grow area has a 14" x 22" filter for passive intake.
pH is low in growing medium, around 6
pH of water is about 7

Picture quality is not great.

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Just checked pH of my water with a new test kit. It's between 6.4 and 6.6
I was using a meter with a probe, earlier. By results from the water test, I would assume that the pH of the medium is even lower.
What is the best way to adjust the water's pH? How about aquarium pH adjusting tablets. One tablet per 10 gallons is the recommendation. That is to maintain 6.8 - 7.2 for aquarium.

Liquid Ph test kits offer the grower an inexpensive alternative to the expensive test meters and give results which are accurate enough to accomplish the task just fine. Usually reading within +/- two tenths of a point (.02) of electronic meters, depending on the kit.

For the grower looking for the most accurate Ph control, there are many various electronic Ph testers available that when calibrated will give extremely accurate readings. Unfortunately for quality units, you may be looking at a higher price than you are able to pay, even the best units will suffer down time as probes go bad. Ph probes are especially prone to failure as the membrane ages, eventually drying out and failing.

The most common solution to fill the void is liquid type Ph test kit.
They're quick, reasonably accurate and very inexpensive.
Great backup in case your probe fails.

When using liquid Ph testers, there are some important things to keep in mind:

Always use a white background when looking at the color in the vial.

A non white back ground can alter the color subtly enough that you may end up being off by anywhere from a little to a lot depending on the color background being used.

Make sure that all color comparisons are done under natural light or normal household lighting and NOT HID light, as the red/blue spectrums of the light (HPS and MH respectively) will cause serious variations to the appearance of the solution, and in some cases you could be running your solution as much as a whole point above or below what it should be.

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What I freely have been given let me freely share

Thanks Mogie,
I did pH tests with a new kit last night.
I started this grow using my ro water from my home.
As the plants were requiring more and more water, and my ro unit is very slow, I started buying 5 gal. at a time from various places around here for 25c per gal.
I tested my home's water. Almost right on 7.
I tested the purchaced water, (5 gal.) So low that 2 aquarium treatment tablets (enough for 20 gal. according to the directions), didn't raise pH enough to change the reading.
Guess I'll reign in my impatience, and use my household ro.
Again, thanks for your time and consideration.

If that's coco you're using it's more than likely a calcium or magnesium problem. Try some coco specific nutrients or find some Cal-Mag.

pH @ 6.2 is great...don't raise it to 7.2 or you may lock out more micros. Treat coco like hydro.....but water less.

I have a couple in straight coco, but the rest are in a mix of coco, organic soil, and a lot of perlite. Coco really retains water, doesn't it?