High runoff pH

Hello DGC. I am on my 3rd grow six weeks into flower. I am growing in a 50/50 coco soil mix. I have been adjusting the pH of my nutrient solution to 6.5, like you would in soil. I just started checking runoff and it is coming out at 7.3. The plants are showing almost no signs of a problem except for a couple leaves at the top that look like they have a mag deficiency. I am at six weeks of flower. Should I water with a lower pH like 6.0 from now on or continue what i’m doing since i’m weeks away from harvest?

4 Comments

Coach Steve on December 1, 2020 at 11:46 am

Chlorosis starting at the top is usually an iron deficiency and typically related to a high pH.

Consider your carbonate sources, that will raise the pH.
What worked for me is doing an acid drench. 4.5-5.0 pH water, 40% soil volume in gallons washed through. Next watering give a full feed at pH 6.2 or below. The lime will buffer up so it’s better to be more acidic. More importantly, be consistent from there. This period of correcting pH will be stressful on the roots and the plant, but once it adapted to it’s environment they should stay green. Avoid inconsistencies in the media by maintaining moisture and a consistent EC so the plant can take up water without needing to fluctuate between making sugars or starch. This is what the roots do to take up water through osmosis.
Inconsistencies in the media and environment is what causes most problems as the plant competes for water and adapts to the concentration of nutrients at the roots.

Mr.eastcoastgrow on December 1, 2020 at 12:32 pm

Far your ph coming out that dosent mean thats what your root zone ph is. Take your going in ph and you runoff ph and find the middle of them and thats your root zone ph more or less. For example if your ph going in is 5.5 and the ph coming out is 6.5 your rootzone ph is around 6 give or take. And the plant can actually change the ph of the media to gain access to a certain nutrient it needs. Certain nutrients are absorbed at a certain ph better than others. We try to stay within a range where all the nutrients are readily available. If I see my plants hungry for a certain nutrient instead of adding more nutrient sometimes I just adjust the ph to where that certain nutrient is more available and easier for the plant to eat. You should be fine.