Freaking out on EC and PPM need help

5 autoflowers 25 days old. About day 16 had a little yellowing of leaf tip on one plant and some yellowing in streaks in a few leaves on another. When transplanted from peat pellets into 5 gal. pots was just watering around seedlings. When they got 8 inches tall decided it was time to wet entire pot. The mix didn’t want to absorb water very well so ended up watering every day for 3 or 4 days. This is just before yellowing appeared so chalked it up to overwatering. Have waited a week and pots getting light so decided to water today. Plants look great, growing gangbusters and no more yellowing or spots. Everythings great I think.
I did a soil slurry test a week ago when I stopped watering to see where I was at. ph 7.0 which I was going to start reducing with next watering. EC was 1.01 which translated to 680ppm.
Before watering today I did it again and pH 6.55 EC was 1.47 which translated to 1040 ppm.
So I watered one plant 1 gallon of water pH 6.6 and checked the runoff which was about a pint. The pH was 5.7. The EC read for ( out of range) the ppm was 9000. I have 2 ph meters and calibrated them and they read close to the same. I only have one TDS meter but my wife has one for our drinking water and it was reading over 5000 ppm. I am going to wait before watering the other 4 in hopes someone will enlighten me as to what’s going on.
My soil mix is : 60% Fox Farms potting soil
20% Bu’s blend Malibu compost
10% worm castings
10% perlite
Fish Bone Meal 3-6-0 1 1/2 Tbsp./Gal. soil
Rose and Flower mix 4-8-4 2Tbsp./Gal. Soil
Azomite 0-0-0.2 1 Tbsp. Gal.
I would think that if ppm was actually that high my plants would be burnt up but they look great. 2 are starting to flower. The plants that I haven’t watered yet are not looking like they are dying of thirst so am going to wait a day or two and see if the one I watered starts showing signs of nute burn.
Any help greatly appreciated. PO

Those ppm numbers sound way off to me. No way your drinking water should be reading that high. I’d check settings and make sure it’s calibrated correctly. Your plants would hate being in a solution of 9000+ppm so it has to be your meters IMO


Thanks for the reply. My drinking water wasn’t that high. The runoff from when I watered my plant was that high. Her TDS meter was reading 5000. Her’s is a cheap one that doesn’t give the conversion factor so it my be different from the one I use. Still really high.

Ordering another TDS meter and calibration solutions for both. Got to be the meter.

To obtain an approximate sodium chloride TDS value, multiply the EC reading (in milliSiemens/cm) by 1000 and divide by 2.

To get an EC value, multiply the ppm reading by 2 and divide by 1000.
Thus, if your EC is 1:
11000/2= 500 ppm.
And if your ppm is 500:
2/1000= 1 EC

So: 1,040 ppm (NACL scale) is 2.08 so something is off on your readings.


My EC reading was oor ( out of range). Sorry if my post was confusing. My spell check subbed (for) for orr. So I have no starting point for your info. I have ordered a new meter. Thanks for the reply.

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