A quick PPM question

When adding my nutrients to the feedwater (5gal bucket water).
So tap water is 130+/- ppm
All my nutrient values are for 1 gal. So I simply multiply those numbers by 5 and then I should be good, but after nutrients are in my 5gal bucket of water my ppm are only at 300… shouldn’t I be closer to 700ppm for my very aggressive veg… it just feels like id be adding WAY too much liquid nutrients… am I missing something… or should I disregard the feedwater ppm and focus on the runoff ppm?

Did you stir it up

Yes I have

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I’ve ran multiple ppm tests. My meter seems to work just fine. I could add more and more liquid nutrients and see if I can get that number up (which I’m sure can happen) I really just don’t want to be burning them.

On my tds meter I don’t use the ppm mode I use us/cm it gives me a better reading I don’t have the conversion chart handy right this second but I’m pretty sure it 1000 us/cm = 500ppm …


What type of meter are you using and on what scale? I recently got my Blue Lab EC/ppm meter and found it had 2 PPM scales. If your using this meter make sure your using the 700 scale.

I use the one you use and I use the us/cm mode

It gives a more accurate reading it took me a minute to understand the whole chart which I found on here not sure if I’m able to copy and paste or not but Here is something I found useful on a different website EC is measured in millisiemens per centimeter (ms/cm) or microsiemens per centimeter (us/cm).

One millisiemen = 1000 microsiemens.

EC and CF (Conductivity Factor) are easily converted between each other. 1 ms/cm = 10 CF

So again, the problem is that different ppm pen manufacturers use different conversion factors to calculate the ppm they display. All ppm (TDS, Total Dissolved Solids) pens actually measure in EC or CF and run a conversion program to display the reading in ppm’s.

There are three conversion factors which various manufacturers use for displaying ppm’s…

USA 1 ms/cm (EC 1.0 or CF 10) = 500 ppm

European 1 ms/cm (EC 1.0 or CF 10) = 640 ppm

Australian 1 ms/cm (EC 1.0 or CF 10) = 700 ppm

Calculating the conversion factor

If your meter allows you to switch between EC and TDS units, your conversion factor can be easily determined by dividing one by the other.

Place the probe in the solution and read TDS in ppm. Change to EC on the meter and read EC in ms/cm.

Conversion factor = ppm / ec.

[Note: ms must be converted to us: One millisiemen = 1000 microsiemens (1.0 ms/cm = 1000.0 us/cm)

According to the chart below:

1.0 ms/cm = 500 ppm (USA Hanna)

1000 us/cm = 500 ppm

Conversion factor = ppm / (ms/cm * 1000)

.50 = 500ppm / (1000us/cm)

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U. K. and (used to be) Canada.

There are Standard Reference Solutions you can buy to double check your meter. Good to have on hand.

What nutrient line are you running?

Veg should be (as you pointed out, in general) around 750 ppm (NACL scale, US). But different solids are not additive but relative (we were just discussing this). I had a meter that would not read table sugar in water.

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Solid start and rock solid Growth Science Nutrients. General Hydroponics cal/mag.
And a couple drops of that real black looking Humboldts Golden Tree.
If you know of any better please let me know I’m open for options.
My meter readings just now are 1050us/cm and 500ppm at 79 degrees Fahrenheit

@Adeezy254 maybe this table will help

I use the same pen HoneForest-white it uses 500 scale
Here are recent pen readings
PPM 1035 us/cm 2202
However something doesn’t convert
1035/ 500 = 2.07EC
however, 2202 / 1000 = 2.2EC oops
Since it converts from EC/us/cm to ppm, maybe the PPM conversion isn’t as reliable


Exactly the chart I have just didn’t know if I was able to copy and paste on the website anyways yeah I don’t think ppm is accurate, when I use mine for example the other day using us/cm was 1068
Ppm was 488

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That’s really the only way to tell. Cheap peace of mind too. Also; buy good tools and they won’t let you down. I finally learned that lesson the last time around.

Not knowing your media, assuming coco; I like to break out supplementing with cal mag on water-only days. This allows me to provide targeted veg nutes at peak concentration (750 ppm NACL scale). Plus I watch runoff and when it exceeds my input it gets water only until it drops below input TDS. That’s just what I’ve found works for me.


The meters work by passing a small current between the elecrodes and measure the electrical conductivity of the metalic ions in the solution ergo things such as chlorine will not be detected. I have never tried to measure sugar in a solution with my Bluelab? Hmmm you know have piqued my curiousity!
In essence, water is not particularly conductive until something else is added to it. Impurities make water more conductive. Though the impurities need to be conductive, some are conductive but are non metalic.

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I have been thinking about upgrading both pens.
Dr Meter ph-100 to Apera ph20, and
HoneForest PPM to Bluelab PPM Conductivity pen
Applicable storage solution
Appropriate selections?

Pure water is non-conductive. Although it could work as a dialectric. Especially if manipulating electrode spacing.

I upgraded to a Bluelab after using less expensive options.

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I very much like my Blue lab pens, have you tried to detect sugar in water with it?

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I haven’t. That happened with a top of the line $13 TDS pen lol.

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