Is this a Potassium or Calcium deficiency?

[Snoop429]

I just posted this in my journal but don't get a lot of traffic so I'll post here as well.

Time for an update and looking for some advice.

My lady got a good watering last night. I gave her 6 liter total which gave me a little runoff. I mixed up the General Organics at a rate the 4 Litter rate plus 10%. Cal/Meg has been at 20% extra for a while now. After I seen damage about 2 weeks ago I had thought it was from the increase in nutrients (They had gotten 6L at full strength) but I think i was mistaken. I'm now thinking that its deficiency from a low ph. I use tap water that sits out usually for 5-7 days before watering. Its naturally 6.8. PPM 245. I didn't start lowering by ph till the week before I started seeing the damage for the first time. Ive noticed it again on a decent amount of leaves. I use the drops to measure ph and find it hard to really know were your at. I wouldn't recommend them. Here are 2 pics of the same leaf.

Even though I just watered yesterday I was wondering if I should flush. (go back to using the 6.8 tap water) If i was to flush how much runoff should i have to get the medium cleared out? and after a flush would you wait for it to dry out again (5 days) before adding nutrients again? Im growing in in Promix with added vermiculite.

After originally posting this in my journal i read a few post and am thinking that maybe my problem is not having my ph low enough and should be trying for 5.5-5.8 it has been around 6. Any feedback is appreciated.

 

[Dan Ultra]

It's definitely not Calcium. Ca deficiency will present itself with tiny spots that look like rust. This looks to either be Potassium or Magnesium. I know you are supplementing Mag, so it leads me more to Potassium. Potassium (K) is typically absorbed in soiless mediums at a pH range of 5.5-6.0, so if your pH has been drifting above 6.0 then you are missing the Potassium uptake. Potassium is also a mobile element, so you will see a deficiency presenting itself in older fan leaves first.

The other thing to take into account is the fact that Potassium stimulate the uptake of other elements (Iron and Manganese) so you might be seeing symptoms of deficiencies in one or both of these micronutrients as well.

-I would suggest getting a reliable digital pH meter and stop using the drops and color chart. It doesn't give you a close enough number to successfully determine the pH needed for cannabis.

-I would also suggest flushing the medium with pH'd water to 5.8. You want to flush with at least 2-3 times the amount of water the pot can hold. Make sure you check your runoff pH to see that it is within a proper range.

Take a look at these charts to assist you further.

 

[PeytonManning]

It looks like it was just a pH imbalance

 

[Snoop429]

Digital Ph meter has been ordered and will flush as soon as i get it. Thanks guys

 

[Snoop429]

I got my ph meter yesterday and also picked up some RO water. After calibrating the meter, tested the RO. 5.5ph. I thought Ro water was a 7 but with it being 5.5 i added just a little of my tap water that was sitting out 5-7 days to get it to 5.8. Plant was flushed with 26 liters of water (just over 4 times my regular amount) The runoff of the last few samples were all in the 6.5-6.6 range. Is this the result that im looking for or should i have runoff of 5.8? Im growing in mostly promix with vermiculite.

Also took this time to do a little trimming. I lost about 8 leaves from damage that fell off on there own and removed others that were showing damage. Under the circumstances id say she looks ok.