HM TDS Meter

[NewToTHC]

Hello:

Have this older HM digital meter and can not find any specifications on it. Wondering if anyone knows if it is a 500 or 700ppm conversion type. Its says calibrate with NaCl which leads me to believe it's 700ppm but maybe wrong?

 

[Bill284]

Hello:

Have this older HM digital meter and can not find any specifications on it. Wondering if anyone knows if it is a 500 or 700ppm conversion type. Its says calibrate with NaCl which leads me to believe it's 700ppm but maybe wrong?

Are you converting to ec?

 

[NewToTHC]

No, not really. Basically looking at the Mega Crop feeding calculator and it specifies feeding rates dependent on EC/500ppm/700ppm meter values. Does it matter at all if just taking a reading or is the 500ppm vs 700ppm meter measure only relevant when converting?

Mega Crop 1 Part Calculator

 

[bluenoserjoe]

Hello:

Have this older HM digital meter and can not find any specifications on it. Wondering if anyone knows if it is a 500 or 700ppm conversion type. Its says calibrate with NaCl which leads me to believe it's 700ppm but maybe wrong?

If it is labeled TDS (total dissolved solids)and is NaCi based then it reads 500 ppm. Confusing as hell as different areas of our world use the different scales so sometimes cross-referencing with different growers is hit or miss unless this is specified. Ec. scale is much easier, in my opinion.

 

[bobrown14]

thought you used dry weight of mega crop to add to water??

 

[copperrein]

There's actually 3 different scales, converting EC to ppm. The two most common are the 500 & 700 scales.

What's the difference between ppm500 and ppm700 scale? The ppm 700 scale is based on measuring the KCl or potassium chloride content of a solution. The ppm 500 is based on measuring the NaCl or sodium chloride content of a solution. The ppm 500 scale is also referred to as TDS - total dissolved solids.

The Hanna scale, ie 500, is probably the most commonly used and what many of the cheaper meters on Amazon are based on.

Info by Farside, quoted from Zayah's thread

 

[bluenoserjoe]

Looks like four scales doing the same thing, although you don't hear much about the cf scale. Looks as though 10 cf.=1ec.=500tds.=700ppm.

20210315_155123.jpg

• bluenoserjoe
• Mar 15, 2021

20210315_155141.jpg

• bluenoserjoe
• Mar 15, 2021

 

[bobrown14]

My brain my brain....

 

[NewToTHC]

thought you used dry weight of mega crop to add to water??

You can, but in my case I think the Mega Crop has probably absorbed moisture from the air so think the ppm is now more accurate.

 

[NewToTHC]

Looks like four scales doing the same thing, although you don't hear much about the cf scale. Looks as though 10 cf.=1ec.=500tds.=700ppm.

EC and CF are the same as far as I understand. Just move the decimal point over or divide CF by 10.

 

[NewToTHC]

If it is labeled TDS (total dissolved solids)and is NaCi based then it reads 500 ppm. Confusing as hell as different areas of our world use the different scales so sometimes cross-referencing with different growers is hit or miss unless this is specified. Ec. scale is much easier, in my opinion.

Sent HM a email, but believe you are correct, most meters in the US are going to be 500 ppm

 

[bluter]

it's still easier to go by weight unless your mc is wet enough to be goo.

mc by ec/tds is finicky crap. the best route is go by the read on your plants, and stick to g/gal.

the mc feed sched is not a written in stone document. it's meant to get you close. stuff will vary.

i have also noticed mc captures moisture over the long term, and is a little less effective. it's not a huge deal for me, as i am in a passive hand watered hydro, and the fix is easy, just add a touch more. i also will use cal mag sometime.

 

[NewToTHC]

HM got back to me and yes it is a 500pm factor

Thank you for reaching out to HM Digital.
If the backside says "NaCl" then the meter is in 0.5 factor.
Let me know if you have other questions.

 

[NewToTHC]

it's still easier to go by weight unless your mc is wet enough to be goo.

mc by ec/tds is finicky crap. the best route is go by the read on your plants, and stick to g/gal.

the mc feed sched is not a written in stone document. it's meant to get you close. stuff will vary.

i have also noticed mc captures moisture over the long term, and is a little less effective. it's not a huge deal for me, as i am in a passive hand watered hydro, and the fix is easy, just add a touch more. i also will use cal mag sometime.

Yes, I typically do. One issue I have with MC being a rather coarse dry mix is that with a small watering feed using just say 1/4tsp and you may or may not get all the nutrients as some of them are in little balls, calcium I think. I took my bag and ground the whole thing up. Not sure if that is the best thing to do, but seems to be ok and would think the whole mix is more consistent.

 

[bluter]

i have found those balls form with a littler humidity over time. they may come back on you.

i stopped tracking ec pretty early on in MC. the system kind of works as a sliding scale, hitting a consistent ec or feeding by it was more trouble than it was worth. i noticed the plants simply fared better when feeding by weight. that is not an option if running rdwc though.