TDS or EC confused

So before I started my grow I did my research on nutrients and TDS well then somebody said don’t use TDS because they use different equations to get the answer where as EC Is the same every time which one should I be going by

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EC (electrical conductivity) is measured in milli-siemens. There are essentially 3 scales in use:

EC of 1 equals 500 ppm NACL scale (US) and equals 700 on Potassium scale (U.K. and Canada).

For example an EC of .1 equals 50 ppm U.S and 70 ppm U.K.

That’s really all there is to it.

TDS can be measured by EC, 500 ppm or 700 ppm scales. TDS stands for Total Dissolved Solids


I also have a pen meter that says it does EC,TDS,TEMP so when I use the ppm I get a reading of 734ppm when i switch it to EC it says 1585 us/cm and the u in us is weird looking. My EC meter on the wall says 1.44 my TDS meter says 680 if the one one the wall is right I’m way high up 980s if the pen is right I’m low. Very confused and yes I calibrated both of them the pen comes calibrated to 364 or something and I purchased a 1000 tds calibration fluid because I was told to calibrate it closer to the levels I needed.

This is the reason I’ve decided to go full organic soil after this grow. No need to worry about
EC/TDS or PPM. Microbes drive soil PH, they balance out the organics within the dirt, the
bacteria and fungus aid the plant in feeding thru a very wide range of nutrients regardless of
the amount in the medium. As long as you have a good colony of microorganisms in the mud
your only worry is keeping the biome alive through the grow.

It’s a pain in the A$$ to start but I only see benefits after the beginning.


Maybe you can help me sir , if you don’t mind
I water my girls with tap water usually PH runs 7-7.4 but when I add the cal/mag and tiger bloom it dumps the PH to 5.4- 6 so I use baking soda to bring it back up inwhich it does. Then I notice that the ppm; are upper 2000but was not before hand

If you’re in soil, anything you water them with
Should be ph’ed to 6.0-7.0pH, (6.3-6.8 being ideal).

Add you’re vitamins and amendments THEN pH your water. And I’d get something way better than baking soda. That’s a salt you’ll need to flush later AND it hurts soil PH.

PH up and down by General Hydroponics is cheap.

Your meter on your wall is on the 700 scale so it takes more ppm to get to 1.44 ec. Your pen reads in micro (u) Siemens/cm and you need to convert that to milli (m) Siemens/cm. You just need to move the decimal point three places to the left. So your pen ec is reading 1.58. Which seems as your pen isnt very accurate because at 734ppm (on 500 scale) should be closer to 1.44 ec. This is why a lot of people only use ec. The different scales of ppm can get confusing.


So what would be the better of them to use that way I’m not fighting with myself going back and forth wondering which one is right or do I need them both and just buy a better set of meters @Bobbydigital

Another question I haven’t been able to get answers . I be had the clones for 3 weeks they were 3 weeks old when u got them right now they are about 15 inches tall I only have another 30 inches room to grow for finished height. That’s as for as I can go up with lights

Neither are deadly accurate but serviceable. Your wall meter should have a reading of 1008 ppm to have an ec of 1.44. Your pen meter should have a reading of 790ppm to have an ec of 1.58. So both are off.

If you have 30” left of grow height before they reach the light then you’ll want to flip now and keep tieing the branches down as they stretch.

When do I start feeding for flower I’m using GH three part micro, grow,bloom and should I cut it in half or go by directions. What should my numbers be during flower

EC is the base measurement to find TDS. You can use either number, but just make sure if you choose TDS you choose the proper conversion factor.

I prefer EC, myself.

Thank you sir