Soil runoff pH problem

My plants are 3 weeks into flower.

They are looking pretty good, but after noticing that they were starting to look a bit off over the last few days i did a soil water runoff test and the pH was at 6, possibly even a bit lower.

Anything that goes into the soil is always pH adjusted to around 7. The water here is quite alkaline and takes a few drops of pH down to get it down to 7.

I need a way to fix this. I've heard of using dolomite lime mixed into the soil but the problem is that i can't re-pot. They are in their final large containers and its too late to re-pot them.

What should i do? Should i mix dolomite lime into the water? Should i stop pH adjusting my high alkaline water during feeds/waterings to try and balance it out?

Lime can be crushed and mixed into your water.

6 is a fine ph and you really shouldnt worry about the ph of the runoff. if you watering with properly phed water and nutes then your fine. also are u using a ph meter or a ph test strips or drops. and do you ph the water with nutes in it

I top dressed mine with lime and watered with straight tap water (7.4 here). Did the trick. Make sure you use fine or 'fast acting' lime though.
The coarse stuff takes months to do anything. I think you wanna go about 1tbsp per gallon of soil. A little more shouldn't hurt anything.

mcpurple said:

6 is a fine ph

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Its borderline... but i think it might even be a bit worse than 6. The fact that i am seeing what looks like nutrient deficiencies indicates that there is a problem and i am pretty sure the pH is the problem. I've had this issue before later in flower but never did anything about it. I really probably should have because it hurt the quality and quantity of the harvest. I'm noticing that they are not drinking anywhere near as much at the moment. Something is definitely wrong.

mcpurple said:

you really shouldnt worry about the ph of the runoff

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This runs contrary to everything i've read... The pH of the runoff indicates the pH of the soil, right? Water sitting in that soil will take on the same pH and a pH of around 6 and below is surely going to cause lockout problems, which looks to be exactly what i see.

Los Muertos said:

I top dressed mine with lime and watered with straight tap water (7.4 here). Did the trick. Make sure you use fine or 'fast acting' lime though.
The coarse stuff takes months to do anything. I think you wanna go about 1tbsp per gallon of soil. A little more shouldn't hurt anything.

Click to expand...

Yeah i can get fine dolomite lime from my hardware store. So you work out how many teaspoons you need based on soil amount and just sprinkle it all on your soil before water? Did you only do it once and thats it or do you apply regularly?

I can't decide whether to try mixing the lime with my water or to top dress.

nizmo said:

Yeah i can get fine dolomite lime from my hardware store. So you work out how many teaspoons you need based on soil amount and just sprinkle it all on your soil before water? Did you only do it once and thats it or do you apply regularly?

I can't decide whether to try mixing the lime with my water or to top dress.

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Yep. I meant tablespoons though. Sorry.
I don't think your measurements have to be exact. A little more or less won't hurt anything.
Use 3 tbsp for a 3 gallon pot, 5 for a 5...well, you get it. Just sprinkle it as evenly as possible
over the surface and water in with water at about 7.0-7.5. I only had to do it once with one
of the plants, but I had to add a bit more for my other two.
I would probably try, like someone else suggested, the water w/dissolved lime first. If that
doesn't work, you could always go back and top dress. Someone else might have a better
solution, but this worked for me. Hope you get it all sorted out.

Cheers that does help me, thanks. Although hopefully someone else can confirm this!

ok 6 is a perfectly fine ph look at this chart it is fine. and to know the ph of the soil should only matter if you think it is really high or low and yours does not seem to low maybe a lil low if below 6 and it seems you dont know the exact ph so i take it your using the strips or drops and not a digi meter. if youve been watering with properly phed water then the runoff should be fine if you know whats going in then you know whats going out.

also what exactly are the plants probs that they have cuz you havent said, also are you feeding them. pics would help alot to figure out the prob you shouldt try to fix something if you do not knw for sure that is the prob

mcpurple said:

ok 6 is a perfectly fine ph look at this chart it is fine.

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Is that for hydro or soil? Because for reasons unknown to me, apparently you want lower pH for hydro and higher for soil.

mcpurple said:

runoff should be fine if you know whats going in then you know whats going out

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What's going in has a pH of 7. Always. But what comes out is a pH of less than 6, and it is getting worse and worse (more acidic) each time i water.

For what you are saying to be true, you would have to assume that the soil itself has no effect on the pH of the water that sits in it, which is clearly not true. pH 7 goes in, and pH of less than 6 comes out. The soil is acidic, and it is making the water i put in there acidic, and this is locking out nutrients which is evident from the apperance of the plants.

You can't tell me that a pH of 6 and below is ok for soil grows!

nizmo said:

Is that for hydro or soil? Because for reasons unknown to me, apparently you want lower pH for hydro and higher for soil.


What's going in has a pH of 7. Always. But what comes out is a pH of less than 6, and it is getting worse and worse (more acidic) each time i water.

For what you are saying to be true, you would have to assume that the soil itself has no effect on the pH of the water that sits in it, which is clearly not true. pH 7 goes in, and pH of less than 6 comes out. The soil is acidic, and it is making the water i put in there acidic, and this is locking out nutrients which is evident from the apperance of the plants.

You can't tell me that a pH of 6 and below is ok for soil grows!

Click to expand...

this chart is for soil hydro you want lower then 6 but im not sure what exact ph for hydro is cuz i use soil.
wgat are you testing the run off with is it a ph drop test, strips or a digi meter. and idint say below 6 is ok i said between 6-7 is ok. if you putting in the properly phed water then it should not be that bad coming out, you are either testing with a crappy meter being the drops or strips. i used to worry about my ph run of in my first grow, i watered with a ph of 6.5 and the run off was reading down in the 4s but my plants were fine so i got kinda scared and asked a much more experienced grower about it and he said not to worry about the run off cuz it doesnt matter, i want a few other opinions and went to a few hydro shops, and nurseries and asked the same thing, they all said dont worry if it goes in at the right ph then its fine. i am done trying to help though cuz you ask for help and then shoot opinions down when givin. i hope you figure it out, in my mind you are having a nute DEF. and just dont know what it is.
hope you figure it out