PPM meter Vs Calculators

Hey everyone, I was looking at ppm and hopefully someday it will make more sense to me. I have a meter and it says it’s calibrated by the mfg so I don’t need to (?). If I use it in some purified water I get about 3 ppm so maybe it’s OK, I don’t really know. But the question I have is comparing what a TDS calculator says compared to what the TDS meter says the ppm is.

If I make a mix using a 32-10-10 plant food this calculator I found online (photo below) says the total ppm will be 589 (plus whatever your water is (so 729 ppm) but using the meter I get a ppm of 365 at 77F in water that started at 140 ppm with a pH of 6.22. I’m in week 4 of vegging and have just been using half of what the mfg. instructions say to use to mix in a gallon of water. The plants look good and healthy but I am probably a bit past the point where I needed to up the ppm. I’m just not sure if I should go by the calculator or what the meter says.

Any thoughts or advice on this would be appreciated. It’s a Zoto TDS meter so it’s not for scientific research :laughing: The meter is reading 1/2 of what the actual is if that gives any clues or may be just coincidence.

Shot of online calculator

HK47 Plant 2 days ago. Its on Day 27.

The calculator doesn’t seem to account for dilution factor of water

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Thanks, and maybe. The site doesn’t talk about it but one of the inputs is tsp per gallon so you would think they are. Ill have to dig around and see if I can find a similar calculator or would you know the math behind those calculations?

That being that stop using online programs.

Start recording your daily routine by date

Watering- ph in/out temp in

Feeding ph in/out. Ppm in/out

Try to do feedings for soil in morning so if need be they can dy out a bit around base of plant

Start trusting your gut! When you see the leaves start changing color up nutrients a bit

Leaves start to burn from tip of them back hold there. If it goes further then tip back off


Problem with that you don’t know if they are relying on water ppm to be 0 or what

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What nutrient line are you using?

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