Ph lockout?

I’ve been growing about a year, and this problem is recent.

I’m in coir using floranova with filtered water. Using about 350w of led in a 2x4 space.

anyway I’ve mostly run indica leaning plants but recent picked up some sativas. Double chocolate and a landrace from laos.

about 6 weeks into flower I start getting rust spots on the lower leaves, which quickly spreads and turns yellow and dies starting from the tips of the fingers.

But this is only on the sativas.




I’ve been using the cheap yellow ph pen off Amazon so I’m thinking maybe it’s off slightly and the sativas are sensitive to whichever way it’s leaning. I just ordered a nicer one but still want to figure this out in the meantime especially if it ends up being something else.

I feed all the plants from the same jug, ppm usually is between 350-650. It’s super dry here so RH is normally around 40%. I feed them at least once a day to run off and keep the ph reading between 5.6-6.3.


anybody know what’s going On? Or recognize what’s happening to the leaves at least?


another thing I just thought of is since it’s gotten colder I’ve been using water from the garage that’s probably like 45-50F. Idk if that could cause problems.

The issue being only on all three Sativa plants is throwing me off.

I can affirm your pH pen is useless. Get some drops or splurge for a good pH meter (>$50).

Leaves have the telltale signs of Ca issues but you do first need to determine if its because the pH is outta whack.

Ok thanks. I do have a nice one and a set of calibration bottles on the way.


i thought it might be ca from the coir and led so I’ve been adding some calmag the past few days but it’s still getting worse so that got me thinking ph.

Ph is also temperature sensitive. So ph at 70 is different then ph at 55f.

How often are you feeding ?
it sounds like your watering cycles may be off

You're in coco. Using filtered water. You're just now adding cal mag. Hmmm. Let's try to figure this out because it's almost certainly not pH related. Seriously.

i feed them every day after lights on and then occasionally again a couple hours before lights off if they’re drinking a lot.

do sativas commonly need more ca/mag or something?


my tap is about 430ppm. I fill an old gallon jug 1/3 way with tap and then mix a couple gallons worth of nutrients in and then use it with the filtered water so I’m assuming whatevers In the little bit of tap was enough for most of the plants.

It’s just odd to me that it’s only the sativas having the same issue and the others don’t have problems.