Measured Ppm Does Not Match Calculated Ppm

[Laredo7mm]

I did a search and couldn’t find what I was looking for, so apologies if this has been asked before. If it has, could you link me to the discussion?

Using hydro buddy I made up a formula of adding 13.5 grams Jack's part A, 5.33g part B, 45ml calimagic, and 20ml GH Bloom. All mixed into 5 gallons of RO water. The estimated E.C. Was 1.5. I measured with my 0.5 scale ppm meter and it came out to be 1500 ppm.

I also mixed up 5 gallons of Jack’s 321 using RO water, 18g part A, 12g part B, and 6g Epsom salts. The predicted ppm should have been around 730, but I measured around 880.

To test the meter, I mixed 1g of kosher salt in 1 liter of RO water and my meter read 990 ppm so it looks like the meter is ok.

What is causing the discrepancy? Are there other things in the nutrients that cause the E.C. to be higher than what is calculated? If there is, how do you mix nutrient strength based on E.C.?

 

[Kot]

I had the same results mixing one gram of lets say calcium nitrate in 1 liter of water. No idea why.

 

[AnselAdams]

I had the same results mixing one gram of lets say calcium nitrate in 1 liter of water. No idea why.

I too am curious, it has been bugging me for a while. I hear tell that there are several different calculations that are used in building meters. Looking asking for real world experiences now. I'll be watching this thread.

Thanks for posting this question.

 

[MeanGreen420]

I did a search and couldn’t find what I was looking for, so apologies if this has been asked before. If it has, could you link me to the discussion?

Using hydro buddy I made up a formula of adding 13.5 grams Jack's part A, 5.33g part B, 45ml calimagic, and 20ml GH Bloom. All mixed into 5 gallons of RO water. The estimated E.C. Was 1.5. I measured with my 0.5 scale ppm meter and it came out to be 1500 ppm.

I also mixed up 5 gallons of Jack’s 321 using RO water, 18g part A, 12g part B, and 6g Epsom salts. The predicted ppm should have been around 730, but I measured around 880.

To test the meter, I mixed 1g of kosher salt in 1 liter of RO water and my meter read 990 ppm so it looks like the meter is ok.

What is causing the discrepancy? Are there other things in the nutrients that cause the E.C. to be higher than what is calculated? If there is, how do you mix nutrient strength based on E.C.?

Calcium will increase ppm a lot I get 340 ppm just from 24ml in 6 gal of ro water

 

[Laredo7mm]

I found some more info about this here: https://www.thcfarmer.com/community/threads/fatmans-diy-nutrient-mixing-guide.20899/

If you go to that link and then follow the first link in the post called “Nutrient Calculator” and then go to the bottom of the page, you will see this:

“If you've tried to reconcile the elemental parts per million (ppm) shown in the nutrient profiles with metered TDS ppm figures, you're probably pulling your hair out by now. In order to avoid confusing the two, it's important to distinguish between their contexts when the term ppm is being used. For more details about TDS/EC metering and how it relates to GH Flora nutrient profiles, see this Cal-O-Rama link (Cal is for calibration).”

Then follow the link for the cal-o-Rama article (sometimes it goes to a weird site) but once you get to the article, scroll all the way down to the bottom and you will see this:

“An interesting blurb from Hydroponic Food Production by Gordon Resh on salts and conductivity:
"Ammonium sulfate conducts twice as much electricity as calcium nitrate and more than three time that of magnesium sulfate, whereas, urea does not conduct electricity at all. Nitrate ions do not produce as close a relationship with electrical conductivity as do potassium ions (Alt, D. 1980). The higher the nitrogen to potassium the lower will be the electrical conductivity values for the nutrient solution."”

So I guess to feed by ppm is not very straight forward if you are trying to use an E.C. meter to measure your nutrient solution strength.