PPM Question?

[CP316]

Hi, I am a new grower, just start testing my ppm and runoff ppm. I just want to make sure my understanding of ppm is correct.
For Example: If I feed my plant with ppm @ 500, so the runoff ppm should be around 500. If it's way over 500ppm, it means too much nuts in the soil, I should feed water next time to get the ppm down. Is this correct? Any input will be appreciated.

 

[Bush Doctor 77]

No! Your drain water will contain salts from previous nutes, and dissolved solids from your media, if you are using soil. For instance, if you pour RO water through peat, it will increase the TDS in the drainage. Just look at it, and it's brown with dissolved solids.

 

[CP316]

No! Your drain water will contain salts from previous nutes, and dissolved solids from your media, if you are using soil. For instance, if you pour RO water through peat, it will increase the TDS in the drainage. Just look at it, and it's brown with dissolved solids.

Thanks for the input.
So it means there is no point testing ppm after each feeding then?
I usually just check the tip of leaves, if there is no burnt, I just keep feeding nuts and add small amount nuts each feed. And when I do see burn, I just water feed next time and feed nuts again after. Am I doing right?

 

[Bush Doctor 77]

I think you would be better off just following a feeding schedule provided by the manufacturer of your nutes. I don't even check PPM when I mix nutes. I just follow the GH schedule, and it works well.

 

[Hdinkleman]

I think you would be better off just following a feeding schedule provided by the manufacturer of your nutes. I don't even check PPM when I mix nutes. I just follow the GH schedule, and it works well.

yep exactly.
i used to check ppms in ppms going out yada yada yada.

i havent touched my ppm meter in months and dont plan to anytime soon either.

 

[vyserage]

Only time I would check soil runoff for ppm is if I wanted to be sure it's not super high for specific stages of growth.

For example if it was 1 month old in veg and runoff was reading 1500 or more, I'd stop feeding and just use plain water for a couple watering before feeding again.

If I saw issues popping up I'd check ppm runoff to see if it shows a surplus or lack of ppm so I can further deduce weather I'm not feeding enough or I'm feeding too much which could cause a toxicity that's locking out something else.
People do say it's pointless to measure the runoff but I disagree to the extent that it gives you an idea of weather you are feeding way too high or way too little. It'll give you a rough idea of what could be going wrong.

Now all that being said, only time I check is if I'm having a defenciency and am curious if I should up the feeding dose. It's usually easy to see if you are overfeeding it due to burnt tips of leafs.

 

[CP316]

Thanks for all the inputs.

 

[Emilya Green]

Thanks for all the inputs.

I will also add that runoff pH measurement is a waste of time in soil too. Think of both readings as coffee out of a percolator... How much runoff gives you a number that means anything? A lot of runoff and you dilute the number, and just a little bit of runoff you concentrate it. This by its very definition is arbitrary. Not to mention what the others have said about soil... how much of your reading is nutes and how much is salts and debris and actual components of the soil filtering through? That is the problem... you don't know. Just follow the nute company's recommendations for ml/gal and don't even worry about PPM. Adjust to 6.3pH right before applying a fluid to the soil, and the soil will drift the mix through the entire pH range, as it was designed to do. Don't over think this... it is not that hard.

 

[Sask420grow]

Your correct in saying if your meter reads a Ppm of 200-500 after testing the runoff you still have nutrients,salts in that soil BUT you can never make it 0. Coco can, but not soil. When you do the two week flush is a good example. People wouldn’t do the flush if they didn’t notice a difference.
So yes, watering soil that has a Ppm of 1000 with water at a Ppm of 0-10, you will drop the Ppm in the soil but it will go back up. Not the same as coco though. Coco has zero Ppm as a base so you can get back to zero.

 

[Emilya Green]

a soil/water solution has a ppm that can be measured. Soil by itself, since it is a solid, can be ground up and divided into an infinite number of parts. The ppm of soil approaches infinity. Any discussions as to the ppm of soil is absurd. Now if we are talking about the parts per million of a certain element within that soil, that is something else. That is why you can measure ppm of the nutrients in a water based system since you know going in the ppm/tds of your water, you can extrapolate what is happening with the nutes. But, unless you can somehow isolate the nutrients out of a soil sample so that you are not also measuring rock dust and carbon and humus and everything else that makes up the soil, a ppm measurement is meaningless.

 

[Oldgrower54]

Thank You for clarifying the ppm subject... it's been causing me fits.

 

[Bush Doctor 77]

You can't measure PPM of soil because PPM refers to "Total Dissolved Solids(TDS)" in a liquid. Soil is always analyzed on a "Dry Basis". You can figure the nutrients in soil, but that involves complicated lab procedures like Total Kjeldahl Nitrogen which includes digestion in hot sulfuric acid and analysis color metrically. Actually, the term PPM needs to be followed by TDS to be accurate.