What is PPM? Why is it important?

I know PPM stand for Parts Per Million. Other than that I’m clueless.

Why is is important? How do you measure? How to correct if not where you want it?

(I’ve got a handle on PH and have a meter, up/down fluid etc)

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Measuring PPM is part of any feeding program using liquid or water soluble nutrients.
Here are two rule of thumb charts showing recommended PPM based on growth stage / age.

I use a Bluelab Conductivity Pen to measure PPM of nutrient solutions.

It is easier to lower ppm of a solution than raise it. If I want the ppm to be 1000 but the mix comes in at 1200, I simply dilute the mix with more water (RO reverse osmosis has zero ppm so it is very effective in reducing ppm. My tap water’s ppm is 180 so I have to use more of it to obtain the desired ppm decrease)


I have never checked ours. Not even quite sure what it all entails. Looks like I’m taking a seat on this one. Learning time :slight_smile:

Thanks for taking the time to respond. Guess I’m still confused.

Sounds like I need a pen like you mentioned.

  • Do I test my feed water (I am using tap and jacks 321)?

  • Other than dilute, how is the ppm increased up or down?

  • Big question, what does knowing the ppm do for you?

(I already know how to test my water for ph. How is this different)?

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I also use Jack’s 321. What medium are you using? It makes a difference as to the pH you adjust to.

I grow in coco so I shoot for a feed solution pH of 5.8

Regarding PPM
With Jack’s, if you measure the components accurately and use the same source water, the solution’s PPM will be very consistent. It will generally be around 1000 depending on the source water and what Jack’s formula you are using.

Yes. After you add Part A, Epsom and then Part B, test the solution’s pH and PPM.
I use pH Up and Down to adjust the pH.
The basic 321 formula of 3.6A, 2.4B and 1.2Epsom should come in close to 1000. Maybe a little less or more 940 - 1060 range. For vegging plants through flower this level of ppm does the job.
As I said previously, if a lower ppm is desired, simply dilute it.
If you want a higher ppm that what the basic formula is, I increase the input values on the front end while mixing. You can increase each component 5%, 10% …whatever you need. If you overshoot the ppm then dilute it.

There are two sides to PPM
the feed ppm. If a plant consistently receives more nutrients than needed, it can cause toxicity in the plant. Nitrogen overload (toxicity) is the most common. Unused nutrients can also accumulate in the medium. This will cause the root zone ph to go out of range. This in turn causes an imbalance in nutrient uptake. (You may have heard the term lockout - this is what lockout is)
Measuring runoff ppm is the other part. The pH and ppm of runoff is typically measured on a regular basis. You get baseline numbers when nutrients are first used. Going forward you compare current runoff numbers with the baseline obtained earlier. If runoff ppm goes up consistently it means the plant does not need all you are giving it. Corrective action is to back off on feed ppm or the medium may need to be flushed. Typically, if runoff ppm is increasing, its pH is usually lower than the baseline pH. Salt based nutrients are acidic and when it accumulates in the medium, the medium’s pH is lowered.
This article explains it much better than I can

I hope I covered the important parts. Hit me up again if I didn’t make sense.


Thanks for the details. I’ll read again tomorrow when I’m fresh and open the link article. Thanks for helping

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In layman’s terms ppm is just a measure of how much stuff is in water. For our purposes it’s how much of whatever nutes are in our water. If you use tap water it also counts all the crap the water plant adds. Bottom line is that ppm is a measure of how strong your nute mix is. The higher the ppm, the stronger. You should definitely get a handle on ppm, EC and NER (nutrient element ratio–NPK/feed charts for your chosen line of nutrients) in addition to pH before starting a grow. It’s a lot better to get a grasp on the basics now than to learn it under pressure or say f it and give up.

@beardless is 100% correct on how to change ppm and everything else in the second post.