SUPPORT TICKET: Low soil PH! 6.8 Ph in and 5.5 - 5.9 Ph runoff

Hello experts!

This is my first grow. I’ve been able to spot WPM and treat it, first with Neem oil (didn’t really work completely), then discovered 40/60 milk/water spray paired with increased airflow and ventilation (Added HEPA filtration system and 2 additional oscillating fans). I also reduced humidity to 35-45% for a few days to make sure the WPM will not come back. I’m amazed by the effectiveness of milk/water spray!!

My current issue is probably low soil PH (maybe N toxicity based on google). I have been feeding the plants every 2-3 days once the soil is dry (based on soil meter reaching dry/moist).
I have a homemade organic soil mixture which should be between 5.4 - 6.3 Ph (I used the ph ranges for each product then calculated a weighted average ph based on the soil mixture ratio (See calculations in photo below)
Soil Ratio PH Range Analysis

-What strain, Seed bank, or bag seed (photo or auto)
Train Wreck, Rocketseeds / Crop King Seeds, auto
-Age of plants
21 days
-Method: Soil w/salt, Organic soil, Hydroponics, Aquaponics, KNF
33% peat moss / 33% Foxfarm Ocean Forest soil / 22% Perlite / 11% Vermiculture / Mycorrhizal Inoculant by DYNOMYCO
-Vessels: Type and capacity of container (fabric, plastic, etc)
12L Smart pot
-PH and TDS of Water, Solution, runoff (if Applicable)
Filtered well water, 6.8 PH in / 5.5 - 5.9 PH in runoff
-PPM/TDS or EC of nutrient solution if applicable
Filtered water - 345ppm
-Method used to measure PH and TDS
PH meter
-Indoor or Outdoor if indoor, size of grow space
Indoor 3x3x6
-Light system List brand and wattage/spectrum
300 watt / Full spectrum Mars Hydro LED (2022 model)
-Actual wattage draw of lights
2.85 µmol/J, High-intensity spectrum with enhanced red(3200-4200K,4800-5000k, 650-665nm)
-Current Light Schedule
-Temps; Day, Night
Day - 75 - 82 F (78 avg) / Night - 71 - 75F (72 avg)
-Humidity; Day, Night
Day: 40% - 65% (50 - 55% avg) | Night: 50% - 65% (55 - 60% avg)
-Ventilation system; Yes, No, Size
Yes, 4 inch inline duct fan 205 CFM / 2 - 6in fans / 1 - 12in fan / HEPA filtration system
-AC, Humidifier, De-humidifier,
No AC, Yes Humidifier, no Dehumidifier
-Co2; Yes, No
No Co2

The smaller plant (left) has a ph runoff of 5.5 ph. This plant also suffered the most from the WPM (i’m guessing lower soil ph reduced the plants immune system).

The bigger plant (right) has a ph runoff of 5.9 ph. This plant also sprouted twice as big as the smaller plant using paper towel method).

Thanks for your support!!

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Welcome to the community! What is the Run off after watering?? The last bit of water coming out of the run off is what you want to measure. That would be the first thing to find out. IMO Seems like the ph is almost there. You want mid 6’s (6.5 ) is great so the plant can feed. :sunglasses: Happy Growing. I’m sure the community will help!

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Thanks Toddr for the intro!
Before measuring the ph, I waited for the runoff to fully pool into the saucer, about 15min after watering. The runoff was about 1 inch high in the saucer. So I guess I did not capture only the last bit of runoff since I measured the entire portion…
How would I collect the last bit of runoff water?
BTW the runoff I measured was 5.5 and 5.9 on each of my 2 plants.

Let the first bit runoff and dispose of it. Then catch the rest lol. I normally use 2 pots when watering just for this purpose…

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Thanks, that makes sense!
I will measure in 2-3 days during my next watering and provide updates.

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A slurry test of the soil mix would tell you what its pH is. The peat product used will have an impact on the soil’s pH. Pro-Mix all purpose peat is buffered with dolomite lime and should have a pH of 5.2 - 5.8.
I imagine you have seen these


Hi beardless,

Thank you for your input. I will look into Pro-Mix for my next grow.
I actually bought, but haven’t used, organic dolomite lime in order to raise the soil ph.

Would you suggest adding dolomite lime on top of the soil before my next watering (assuming my soil ph is less than 6.0)?

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Dolomite lime is quickly becoming my goto recommendation for pH being too low. Its pretty effective if not the fastest acting. Be sure to give it a week after amending (at least) before adjusting more.


Thanks PurpNGold, I mixed 6 TBSP of Organic Dolomite Lime to each 3 gal smart pot. I spread it evenly and mixed into the top 1-2 inches of soil then watered about .75 gal per pot using filtered well water which has a ph of around 6.5 - 6.8.

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Keep me posted on whatever comes next. Happy growing

Hi PurpNGold,

Keeping you posted as requested :slight_smile:
The dolomite lime worked completely, the runoff is now between 6.8 - 7.0 ph!

New Questions:
1) I plan to perform a foxfarm sledgehammer flush using BobbyDigital’s method (see quote below).
I have 3gal smartpots, regarding watering amounts, do you recommend 1 gal of sledgehammer mix, then 2 gal of plain water, then water with 1 gal of nutrient solution? (I start to get runoff around .75 gal.)
2) Next, Foxfarms schedule says to use Grow Big well into flowering, but the bottle says to stop at flowering. What do you recommend?

Using zero ppm water, from my new filter, I plan to use BobbyDigital’s method from a IGLM post in 2019:

This post was from Day 21, it is now Day 30 (see Day 30 photos below)

After adding 6 TBSP of dolomite lime to the top of the soil, I watered with the 6.8ph filtered well water. I also watered 2 additional times before the photos were taken (See calendar below). Second watering I started adding foxfarm nutrients. I had trouble keeping the EC and ppm down because my water is 444ppm even after filtering and I used potassium bicarbonate to ph up the mix.
My latest watering I was able to capture final runoff and by dumping the original runoff. My final runoff was EC 3800 and ppm 1888 (very high I know); I also just purchased gro pro pot elevators because I learned that I shouldn’t let the pot sit in the runoff which is what I have been doing. Therefore, I’m sure I just need to flush once more in order to lower my ppm and EC.

Tomorrow, Day 31, I plan to perform a sledgehammer flush since I will be using foxfarm liquid and dry nutes. Also, I want to make sure I remove the salt build up at the bottom of the pots from letting them sit in runoff several times over a few weeks (before learning I shouldn’t do that! lol). I also just found an amazing water filter (ZEROWATER) which reduces the ppm and EC to virtually zero!


There’s actually a better way now. Mix up the sledgehammer and pour twice your normal watering. Then discard runoff and let the soil dry out like normal. Then you can continue feeding when it dries out. Unless it’s your final flush.


Thanks Bobby,

This is very helpful and much less time consuming!

So no need to add plain water after the sledgehammer water.
I was also wondering about feeding right after watering and if it should dry out, this also answered that question.

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Nope, let the sledgehammer soak for the three/four days it takes to dry out then continue your feed regimen


They are looking good! Happy you got ur pH up. Now follow Bobby’s solid advice and ull be on cruise control til harvest (hopefully :wink::joy:)

Day 32

Before Pruning

After Pruning

Close up of small bud that was pruned