My medium pH is 6.2-6.5. Do you either of you guys feed every watering or do you ever do a watering in between? I also took a few handfuls of pro mix out and put it in an empty cup with holes and measured the EC of the runoff to see if there was a buildup already. It measure 0.4 so I don’t think there is. Are you also using the HP version? I am still having a hard time wrapping my head around the whole pH vs water alkalinity thing. I wonder how useful a soil EC probe could be.
Here’s a copy and paste from the emails with the pro mix person:
Hi
Thanks for your interest in our products.
First, Pro-Mix is a soilless media and is a bit different than coir, actually it’s more forgiving. It doesn’t hold as much salts as the coir.
Pro-Mix Hp soilless media is amended with a starter charge and limestone in order to keep the pH at 5.8-6.2 during the crop.
If you are using a pH meter, be sure you have it calibrated, this can cause wrong readings and can lead to the wrong changes.
If you use Cal mag or other fertilizers with a lot of calcium, this can drive the pH up too high.
So first I would check if your pH in the soil is around 7, if so, it’s too high and your plants can’t pick up Iron or Phosphorus as much as if your soil had a pH around 6.2.
You acidifiying your water, but maybe you don’t need to. Acidification neutralizes calcium carbonates, but if your water has an alkalinity of 30 mg/ l, before acidification, that is not a very high alcalinity. I know the pH might appear high, but it’s the calcium carbonates in the water that drives the pH up.
*Try another fertilizer with less potassium, potassium is good but for end of the production cycle, but at first you need nitrogen for the vegetative growth. *
There’s a lot of fertilizer companies, that have good products, but you have to use those that are adapted to your soil and water. Did you ever use 20-20-20 at a week dilution 1g/l . This fertilizer is easy to find and not very expensive.
This is a good fertilizer to start with and after the vegetative growth is in full swing, then cut back to a fertilizer that you are using , like the Jacks hydro.
See the link below for more ideas that can explain your issues.
How to Maintain the Proper pH of a Growing Medium | PT Growers and Consumers
From the pictures I see, you’re right, it appears more like a stress, too much salts or not enough nitrogen and the yellowing at the top growth is often iron deficiency.
If you go to your local garden center, they might be able to help you with your fertilizer and measure your soil pH and EC to see if its similar to what you are measuring.
Best of luck.
and this is the second reply:
Hello
Citric acid can definitely neutralize Carbonate calcium in the water and in the soil.
*The water pH and soil pH are not really related in soilless peat media. The carbonate calcium is what makes the pH go up in soil so even though the water PH is high it doesn’t mean the water has a lot of carbonates.
I think you should be good but don’t acidify too much in the fertilizer tank it could lead to other issues, like precipitation of some salts. try to keep it close to 6
Edit: I wonder if me leaving out magnesium sulfate is causing some imbalance?The jacks label says potential basic: 170lbs of calcium carbonate equivalent per ton. I’m unsure of the charge of calcium nitrate and magnesium sulfate.
I really want to figure this stuff out though because it is 4-5x cheaper than coco where I am. Sagging leaves, lightening colour and generally at a standstill. The aunt lemon (yellow tag) are looking the worst out of the bunch but all of them especially in the big tent are suffering.
Maybe I’ll buy a bag of 20-20-20 for veg after all.
Paps
