Autoflower soil Low PH Runoff with high ppm

Hello All, Im still kinda a beginner and am having trouble with my grows. This is my second round of AutoFlowers and they are almost in week 8 and they look like i have a calcium deficiency BUT after checking my runoff my PH is at a super low 5.3PH and it went in at 6.5.

So after reading around I was under the asumption I needed to mix in the soil a little Dolomite Lime so in each 5gal pot i mixed in 2tbl of the lime the best i could AND I purchased a Bluelab TRUNCOMV2 Commercial Truncheon Nutrient Meter.

The meter came in today and they were ready to be watered so i tested PH and ppm before the water went in and its runoff. The results are below, how can i fix this? Thanks!

Water + HP Trio @ 6.5ph
1.3 ec 910ppm (ECx700)

Water Runoff @ 5.2ph
3.2ec 2240ppm (ECx700)

Fox farm Ocean Forest
5 gal Air Pots
4- 1200 full spectrum LED
GH FloraMicro 1/2 tsp per Gal
GH FloraGrow 1/4 tsp Per Gal
GH FloraBloom 1/2 tsp Per Gal
GH CalliMagic 1/2 tsp per Gal
Humidity 50-51%
Temperature 79-82


I expect you have a salt buildup, as this will submarine your pH. FF soils correct to ~6.5 with a good flush.


I forgot/thought I mentioned (sorry) I did a good flush a several days ago before anything and these are the results after today.

Should i flush again? Also you say salts, am I overfeeding?

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By good flush do you mean 3x your pot volume in ph stable water ph’d to 6.8?

Possibly but thats not what midwest means. When using synthetic nutes to feed with they leave behind salts. This salt will build up and cause your ph to drop. Ph is important, if not in a good range nutrients will get locked out .

Your figures are confusing. E.C. and PPM represent the same thing (tds or Total Dissolved Solids) but I dont see your PH anywhere. A pic of your plant and the ph value of your runoff will help answer this question alot.

Welcome to the community.


welcome to the community, a pic would be great like @Docnraq stated.

Ok all I took a picture for ya of the ones doing it. I bought the bluelab Truncomv2 meter because it gave me all the values in a row with a light indicator. The values I gave were from testing the water that I ph’d to 6.5 after adding GH and then the second set of values I gave was what i got from the runoff.

Water + HP Trio @ 6.5ph
1.3 ec 910ppm (ECx700)

Water Runoff @ 5.2ph
3.2ec 2240ppm (ECx700)


I’m not familiar with that model, what’s the results using the 500 scale :love_you_gesture:

1600, its right there pic 2 at his thumb. It’s a great meter I have one that has to be at least 20 yrs old from the hydro days and still works, loose accuracy is close enough in EC/TDS. I mostly use my handheld cuz I’m not mixing 55 gal at a time these days.

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Appreciate that Brother and good to hear from you :love_you_gesture: couldn’t see which one had the light on

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Yeah thats the annoying thing with that style, “no hold” at least on my old truncheon, once out of solution about 3 seconds to make mental note if its blinking between 2 or holding on one.

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Man I was high last night. Totally missed the PH there.

If you pour 900ppm feed into the pot and comes out @ 2000ppm then you feed when you didnt need to. This will lower your ph. Same reason that you can start with water at 7ph and have to add ph up after adding the nutes in.

Contrary wise, since this is after a flush seems you didnt flush enough and there is still alot of nutes in your soil then you added more. The state of your leaves suggest you have been outta whack for a lil while. When your soil dries, flush again. This time flush slowly, (water should be phd to 6.8 and be under 500ppm) pour in a gallon and wait till it drips out then another and another. Check runoff after every 5 gallons until the runoff ph and tds is in range. (6.5-6.8ph and tds that resembles your flush water.) Once that is achieved, mix up a feed. Wait until water stops dripping from the soil (takes 10-15 mins) then SLOWLY pour in your feed. (If runoff comes out the side of your pot you are pouring too fast.) Record runoff ph and tds. This should fix your ph issue and resolve the lockout. Your leaves look as they do because your plant has been cannabalising its leaves due to the lockout of phos and potassium (P and K) to make your flowers.
They will never go back to green.
It takes about an hour total time to flush a 5 gallon pot.

Should look something like this on paper

The bottom 3 figures are 1) runoff and tds after final 5 gallons flushwater 2)ph and tds of feeding solution going in to soil and 3) ph and tds of feeding solution runoff

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Ok thanks! What temperature should the water be that I flush with?

Room temp, not warmer then say 75-80 degrees.
Know that runoff isnt exact representation of rootzone ph and tds, its just a loose figure but it still needs to be close to what your looking for.

Ok, 3 need watered so im flushing now @ 6.8ph. now just to be clear I continue to flush very slowly until my runoff is at the 6.8 pH? Once this happens, I water my girls with my nutrient solution checking the PPM before and after. Or should I let them dry out and water checking the PPM before and after along with the pH to see if the roots are taking in the nutrients when they do take in the nutrients does that mean my PPM will be lower than my runoff PPM?

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Yes, it will take at least 3x the volume of your pot (5 gal pot will take 15 gallons water or more) in water ph’d to 6.8 and having a minimum of 350ppm total disolved solids (tds) in it.

Yes, always record the PH and TDS of nute solution/ water and runoff. It is most helpful to have record of the trending direction of ph and tds

Do let the water drip out after each few gallons of flush water, this helps the next few gallons to penetrate the soil further pushing out the salt build up. Also let the final flush water drip out (takes 5 or 10 mins) before feeding. This all done in the same session.

No, your runoff ppm should always be lower then your feed ppm (when feeding) water only days should be lower ppm going in and higher coming out. Once water only day runoff gets below 1000 ppm its time to feed your plant.


Lemme know how it turns out. I am always happy with hiw my plants look the day following a flush.

Sure will… I have another question well actually two more when I water with the nutrients after this do I just water till I have some runoff and then I’m done until it dries and question two is it sounds like this is a normal thing to flush a plant is it? Does it happen often or should it?

Thank you so much for the help I knew this form was awesome I read through a lot of posts before posting and it seems everybody helps everybody!


Not exactly. Because the soil is really wet (from the flush) it will begin to runoff right away. Just use the same amount of liquid you would normally feed with. I.E. my 5 gal pot takes 1 gallon of water to get 15% runoff so after the flush I use 1 gallon of feed solution.

This is a matter often argued. There are many ways to skin this cat so one is not really better then any other just different methodology. That being said, I am team flush. The nutes I use (FoxFarm trio and pk boosters) has 3 flushes in the schedule between weeks 4 & 5, 7 & 8, 10 & 11. I follow that. My plants love it they always look refreshed and when runoff is in range I am stress free. Each growth phase has a different need in the ratio of N P K. Flushing the soil resets it and allows me to reintroduce the propper ratio for the phase they are in.

You are most welcome. This is the nicest forum on growing in my opinion. Disagreemnets are fine but comfrontation and all that goes along with it are against forum policy. Free exchange is how we keep homegrowing alive. Without it, the dispo is our only access and that can never happen.


@SoggyCashew how did things turn out?

Can I jump on this thread as I’m having the same issue. I have two 4x4 grow tents. One has 3 plants in 5 gallon cloth pots. The other tent has 4 Bruce Banner plants in 3 gallon air pots. My plants were not looking good and the good people on this site advised flushing for me, too. And you’re not kidding about this process taking tons of water!!! Instead of listing values for all 7 plants, I’m just giving a range. Before the flush the initial runoff ph was between 5.95 and 6.16 for all plants and tds readings were all above 2.15. After flushing, the runoff ph for all plants was between 6.21-6.41. Tds runoff ranged from 972-1.100.

I know I’m supposed to get the runoff ph close to 6.8. Is there anything else I can do to get the runoff ph higher? The input ph for the flush was 6.8, with TDS of 279(tap water). And do the Tds numbers need to go lower? I’m in the 3rd week of flower, btw.

Thanks in advance!