High soil pH 7.8, and what I should do about it...

[ffgrowery]

Hey guys, I'm posting this question on several MJ forums in order to get some different opinions on this topic.

Details about the grow:

• 4x4x6 tent
• 1000W HPS light, running %75, recently lowered to about 21" above plants.
• AC Unit set to go off at 75
• Temps have been between 68-78F (20-25C)
• Humidity between 35%-60%
• RO Water pH 6.0 with CalMag 1tbs/gallon. No neuts yet.
• Recently transplanted from 4" pots into 3 gal. Air pots.
• Soil is FFOF

I have recently re-potted my plants into 3 gallon air-pots, filled with FFOF soil. I have watered with pH 6.0 water, and let the runoff sit for a day. Once collected, the runoff tested pH 7.8! Before you ask, I'm using an electronic Oakton EcoTester, and I've recently calibrated it.
This worries me because I'm afraid that the actual soil pH is somewhere well above 8, and that it might cause nutrient lockout soon. The plants are looking pretty healthy, although some of the plants are significantly shorter than others, and are slightly more yellow.
Here's what I am thinking of doing. I am all for doing a flush in hopes of lowering the pH, but instead of wasting a ton of water, I'm thinking of collecting the runoff, lowering the runoff with pH down, and running it through again. Does anyone see a problem with this? I'm considering it might be good to recycle the runoff, and put all of the nutrients in the FFOF back in the soil, while lowering the pH.
Has anyone tried this? Would this work? I'm in Cali, and with the drought, I feel crappy simply wasting runoff water. I've also heard of people adding vinegar, or lemon juice to their water in hopes to raise the acidity. Any alternatives, or other solutions to this problem are welcome!

 

[ffgrowery]

I did not. As far as I have read, FFOF is good for about 3-4 weeks without any added nuts. Then I plan on starting the feed. Would you recommend otherwise?

 

[ffgrowery]

of the runoff? If yes, then yes, I ran it through a coffee filter, and it showed 7.8 pH, and ~1300 ppm.

 

[cannapits]

fox farm soil runs a little hot sometimes IMO. I wouldnt feed them anything yet. Id work on bringing the ph down a tad. 6.5-7.2 was always a sweet spot for my soil runs. but never had issues at 7.5

 

[Mr_GreenGenes]

I would NOT re-water with your runoff. I've always noticed my runoff PH to be much lower than what I put in. If I were you I would add 1 cup of pulverize/powdered Dolomite Lime to every cu. ft. of OF. It will help keep that PH from climbing above 7.0. Good luck. MGG

 

[Seamaiden]

Hey guys, I'm posting this question on several MJ forums in order to get some different opinions on this topic.

Details about the grow:

• 4x4x6 tent
• 1000W HPS light, running %75, recently lowered to about 21" above plants.
• AC Unit set to go off at 75
• Temps have been between 68-78F (20-25C)
• Humidity between 35%-60%
• RO Water pH 6.0 with CalMag 1tbs/gallon. No neuts yet.
• Recently transplanted from 4" pots into 3 gal. Air pots.
• Soil is FFOF

I have recently re-potted my plants into 3 gallon air-pots, filled with FFOF soil. I have watered with pH 6.0 water, and let the runoff sit for a day. Once collected, the runoff tested pH 7.8! Before you ask, I'm using an electronic Oakton EcoTester, and I've recently calibrated it.
This worries me because I'm afraid that the actual soil pH is somewhere well above 8, and that it might cause nutrient lockout soon. The plants are looking pretty healthy, although some of the plants are significantly shorter than others, and are slightly more yellow.
Here's what I am thinking of doing. I am all for doing a flush in hopes of lowering the pH, but instead of wasting a ton of water, I'm thinking of collecting the runoff, lowering the runoff with pH down, and running it through again. Does anyone see a problem with this? I'm considering it might be good to recycle the runoff, and put all of the nutrients in the FFOF back in the soil, while lowering the pH.
Has anyone tried this? Would this work? I'm in Cali, and with the drought, I feel crappy simply wasting runoff water. I've also heard of people adding vinegar, or lemon juice to their water in hopes to raise the acidity. Any alternatives, or other solutions to this problem are welcome!

You want to drop pH. You can do that with sulfur, but I personally think you shouldn't mess with it. You could pH your feed water down into the mid 6 range, but depending on your source water that pH could bounce due to alkalinity.

I would absolutely *not* add dolomite lime in this scenario. IME dolomite lime can buffer pH up towards 8. That carbonate molecule attached to the Ca and the Mg won't let pH drop much further below 7, either, again IME. Peat would be more helpful here for naturally buffering pH towards the acidic instead of the basic.

Also, stop using run-off to test parameters. Use the slurry method, very simple. You take several samples of the soil you want to test and mix those. You get a sample of 0EC water, test its parameters to be sure of those (pH in this case). Mix enough soil into the water to create a loose slurry. Let it set for 7-10mins (I have not found that letting it sit any longer changes readings), then re-test. Those results are much closer to what's actually happening in the root zone.

Don't chase numbers, either.

 

[ffgrowery]

You take several samples of the soil you want to test and mix those. You get a sample of 0EC water, test its parameters to be sure of those (pH in this case). Mix enough soil into the water to create a loose slurry. Let it set for 7-10mins (I have not found that letting it sit any longer changes readings), then re-test. Those results are much closer to what's actually happening in the root zone.

Don't chase numbers, either.

Thanks for the advice. I have RO water which after tested has about 20-30ppm straight out of the RO filter. I'm assuming this is what you mean by 0EC water? Low ppm so low conductivity? I'll definitely try to do the slurry method and see what I get back with.

How do you recommend I apply peat to my pots? Just sprinkle some on top? Mix it into the top soil?

Good advice on not chasing numbers too. Should keep my eye in the big picture here, not miss the forest for the trees :)

 

[Seamaiden]

Yes, exactly! You can use the peat two ways, on top of the media as you're thinking, OR you can pass the water through to drop the pH a bit. It's a more tricky process than just adding pH-down, so if it's easier to just push the pH down prior to watering, do that. Peat is a "soft" method I've used for fish as a filtration media, it 'grabs' carbonates.

 

[Mr_GreenGenes]

I would absolutely *not* add dolomite lime in this scenario. IME dolomite lime can buffer pH up towards 8. That carbonate molecule attached to the Ca and the Mg won't let pH drop much further below 7, either, again IME. Peat would be more helpful here for naturally buffering pH towards the acidic instead of the basic.

To each their own. I've used the extra lime for years with all FF soils, 1 cup per cu. ft. of medium. I don't have any problems with high or low PH. I've also given the lime advice to others having similar issues and it helped greatly. MGG

 

[Seamaiden]

So, they've had high pH problems and the DL brought it down? It seems that has never been my own experience, with or without testing. :)

 

[Mr_GreenGenes]

Guess we all have different experiences Sea, doesn't mean one is more right than another, just means they're different. I've used powdered DL for YEARS and never experienced what you're speaking of. MGG

 

[Don Peppy]

I think it helps buffer the soil, and keeps it from getting to high or to low.. I add it to my soil from the get go.. It probably won't help bring down the soils ph when adding it later on down the road.. It keeps my soil in the sweet zone..

 

[ffgrowery]

Huge thanks to everyone who replied. This is my first grow so I am learning. I now realize that adding dolomite lime to the soil beforehand helps keep pH in line.

I also did the slurry method as per Seamaiden's suggestion. The pH of the water going in was a neutral 7, 20 ppm solution. After letting it sit in the slurry, the pH of the soil was around 6.8! This tells me that actual pH is probably closer to 6.6, which is pretty perfect. The plants are doing well (one grew 4" in the past week during Veg), so I'm just going to sit back and enjoy it!

Thanks again!

 

[burn4me]

Huge thanks to everyone who replied. This is my first grow so I am learning. I now realize that adding dolomite lime to the soil beforehand helps keep pH in line.

I also did the slurry method as per Seamaiden's suggestion. The pH of the water going in was a neutral 7, 20 ppm solution. After letting it sit in the slurry, the pH of the soil was around 6.8! This tells me that actual pH is probably closer to 6.6, which is pretty perfect. The plants are doing well (one grew 4" in the past week during Veg), so I'm just going to sit back and enjoy it!

Thanks again!

sounds like PH is good to go bro. and i add DL before hand when i mix up a batch. it has done great at keeping my PH from getting low since i use peat base. glad its smooth sailing for ya now.

 

[Seamaiden]

I no longer use DL, I rely on my heavily carbonatated water. Yes, I made that word up. Carbonatated.

 

[ffgrowery]

Carbonatated.

HAH!

All plants have grown at least 3 inches (some up to 4.5) in the last week. I thinking things are fine!

 

[Bannacis]

I've had great results using dolomite lime, but only added to my soil mix and allowing it to cook with the rest of my ingredients before planting. not to put in soil after plant has been growing in pot for a while. its a buffer not a ph up or down. imo...

 

[SmokinSteve]

I'm glad that your plants are looking up!

As with all new growers you will run into some problems big or small but the lesson here is to be proactive. Dolomite lime is a great pH adjuster to add at the beginning of your grow. The medium I use, PRO-Mix HP, has dolomite lime present in the mix so I start seeing its benefits from the beginning even before I see any pH problems.

Good luck with your grow!

 

[burn4me]

I'm glad that your plants are looking up!

As with all new growers you will run into some problems big or small but the lesson here is to be proactive. Dolomite lime is a great pH adjuster to add at the beginning of your grow. The medium I use, PRO-Mix HP, has dolomite lime present in the mix so I start seeing its benefits from the beginning even before I see any pH problems.

Good luck with your grow!

so may i ask you aquestion? you add no extra DL to the mix? you have no PH issues? im a promix user myself. so i was curious.

 

[SmokinSteve]

Right I haven't needed to add any extra. You can come across pH issues but it's good to foresee those problems by adding what you can in the beginning. How much DL do you add?