How to test runoff ph

I have been wondering how to calibrate the ph coming from the runoff. I water at a 6.4 ph and just checked runoff and it is 4.9. Is this normal?

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No, you soil is very acidic. You need some (Dolomite) lime or a very base solution
to help lower the acidity. Baking soda helps but it’s a salt, too much will ruin your soil
and you need to be careful doing it.


What size and type pots are you using?

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• What strain, Seed bank, or bag seed
• Method: Soil w/salt, Organic soil, Hydroponics, Aquaponics, KNF
• Vessels: Pots, Grow beds, Buckets, Troths
• PH of Water, Solution, runoff (if Applicable)
• PPM/TDS or EC of nutrient solution if applicable
• Indoor or Outdoor
• Light system
• Temps; Day, Night
• Humidity; Day, Night
• Ventilation system; Yes, No, Size
• AC, Humidifier, De-humidifier,
• Co2; Yes, No
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• Bag seed

• Method: Fox farms ocean forrest with 1 lb of live soil mixed in bottom 3rd of pot
• Vessels: 5 gallon fabric pots
• PH of Water, Solution, runoff 4.9
• PPM/TDS or EC of nutrient solution I dont know
• Indoor
• Light system mars hydro tsw 2000w equivalent led

• Temps; Day is 79 to 81 and 72 at night
• Humidity; around 50% all the time
• Ventilation system; Yes 4 inch vented out of tent and into attic
• I have ducting connected to my ac vent in room Humidifier yes, De-humidifier yes
• CO2 no
Nutes- fox farm trio cali magic fish sh!t and Hawaiian bud boost used in flower

1 plant is better lookinh than the other

I would probably top dress each pot with about quarter cup of fine dolomite lime, and work into top of soil some. Then slowly pour about 10-15 gallons of water ph’d to 6.5 through each pot. You can collect last little bit of runoff to see how much ph comes up.

Would probably be a good idea to get something that will test concentration of your nutrient solution in and out.


Community has got you covered. I just like to add I would verify my pH meter with a fresh bottle of pH 7 solution. Overall plant looks happy.


So you are saying to flush the soil? 10 gallons per plant
seems like alot of water.

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Yes it is. Standard flush is 2 to 3 times the vessel’s capacity. You need to use enough to purge excess nutrients and as dbrn32 instructed, incorporate lime to act as a buffer.
If your ph out is 4.9 that means is actual soil ph is probably less than that.
This a reference guide to soil ph and nutrient availability. The plant can not take up much at 4.9

Personal experience. I made it through my first couple of grows without ph-ing anything. It was just dumb stubborn luck. On the third grow, the plants were a different strain and a little more sensitive to my neglect. I started loosing plants. I am now nearly compulsive in that nothing goes in without checking Ph. That includes soil - learn the slurry test. I would add a little lime to my FF OF on the front end - a couple weeks before using.
Make sure your pen is calibrated and accurate. Then take corrective actions.
Good luck.


Do I add the lime before or after the flush


Before the Flush scratch in on top of the Soil.


Also how did my soil end up acidic? FFOF comes ready to use and all my waterings were PHd to a range of 6.2 to about 6.7

As acidic as 4.9 is, it seems really off. Usually the soil ph drops because of unused nutrients building up in the soil. The general rule is if the runoff ph drops .5 from where you start, it is time to flush. A second option, and your situation is more than likely a combination of the two, is your bag of OF turned. There is is bunch of living stuff in those bags and sometime the ph drops more than what the buffering agent used would dictate. Did I mention soil slurry. This is a reason for doing a slurry before sticking plants in it. Remember I said something about being compulsive. Maybe obsessive or fanatic is more accurate.

When you water do you water enough (including with nutrients) to have 10 - 15% runoff? Causing runoff seems like a waste of nutrients but there is a reason for it. 1. is to get a good ph reading and 2. is to flush through some of the nutrients that would otherwise accumulate and turn the soil acidic.
Here are a couple of articles I found to be useful I stuck <> in so it isn’t a direct link that will get censured.



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You got it, just like the others have suggested as well.

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Flushing now, what should runoff be when flushing with 6.5 ph water?

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Do these readings look normal?

Cool…guess I’ll wait and see