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Testing PPM

Posted by hendu2875 none (My Page) on
Tue, Mar 25, 14 at 19:39

I have this TDS tester.
It only measures ppm
Says it was calibrated to 500 us/cm

My question is. When I read it and it says
1400 ppm. Is that the actually ppm of nutrients
Or do I need to use a conversion factor?

What nutrient chart do I go by for best results?
They all seem so different.

Thanks.
I'm using masterblend 4-18-38. Mixed with added
Calcium nitrate to bring me to a 20-18-38 npk

Masterblend says to mix 12 grams per 5 gallons
But was wonderig what nutrient chart to use if I want to
Use them.

Thanks.
Brad from mi


Follow-Up Postings:

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RE: Testing PPM

Hi,hendu2875
That seems very high PPM in the finished solution.
My finished solution newly mixed is 673ppm and that equals approx. 1345 uS EC
My base water from the tap is around 191ppm 384 uS EC

Hey have you been watching Bobby Hydroponic videos on You Tube?

Glen

This post was edited by Astaroth on Wed, Mar 26, 14 at 21:13


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RE: Testing PPM

Yes I've watch his vids
I'm confused on the ppm then.
I thought I wanted around 1200 ppm for the
Nutes. My well water is 134-145 ppm


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RE: Testing PPM

I believe if you divide the reading by 500 you'll get the EC measurment.
Then you mix your nutrients to a known concentration and "calibrate" the meter to what is actually there.
I.e.: if the meter reads 1200 but you know the nutrient is 1400, you calibration factor is 14/12.


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RE: Testing PPM

I looked at this and just decided imo the 'ppm tester' was bad if the mix was done right. I think he really did have an *EC* of 1400 uS/cm, not ppm of 1400 (=EC 2800), but according to his economy version tester, it was ppm. If you are mixing correctly, that is putting approximately 30 grams (MB+CAN+Ep) in five gallons of the sort of water you mention, I would just consider the numbers EC (1400 uS/cm = 1.4 mS/cm), and forget ppm and start using EC so you don't get twisted up with conversion factors.

I agree the ppm stated is way too concentrate to make sense if no error was made in diluting the powders.


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RE: Testing PPM

SEEDLING PLANTS
a. 100 gallons of water
b. 8 ounces (1/2 pound) of CHEM-GRO 4-18-38
c. 4 ounces (1/4 pound) of Calcium Nitrate
d. 4 ounces (1/4 pound) of Magnesium Sulfate
e. Adjust pH to 6.5
f. Conductivity 1200ppm + source water
( 1.60 mhos + source water)
SECOND FLOWER CLUSTER
TO 4TH FLOWER CLUSTER
a. 100 gallons of water
b. 8 ounces (1/2 pound) of CHEM-GRO 4-18-38
c. 8 ounces (1/2 pound) of Calcium Nitrate
d. 4 ounces (1/4 pound) of Magnesium Sulfate
e. Adjust pH to 6.2
f. Conductivity 1500ppm + source water
( 2.00 mhos + source water)
AT 4TH CLUSTER OF FLOWERS
AND OLDER PLANTS
a. 100 gallons of water
b. 8 ounces (1/2 pound) of CHEM-GRO 4-18-38
c. 8 ounces (1/2 pound) of Calcium Nitrate
d. 5 ounces (.31 pound) of Magnesium Sulfate
e. Adjust pH to 6.2
f. Conductivity 1700ppm + source water
( 2.27 mhos + source water)

Straight from the Fertilizer Company
So are you saying my METER when it reads say 1400, its not actually PPM but 1400US/cm? Considering thats what it says it was calibrated to..


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RE: Testing PPM

I'm not saying anything because it is unconfirmed to me exactly how much fertilizer (grams 4-18-38; grams Calcium nitrate, grams magnesium sulfate) you put into how much water (gallons or if you prefer liters) which correspond to the measurements (water ppm alone and water+3 nutrient powders ppm(think you already gave) all total (clarified if it includes the water). If you would like to get to the bottom of it, that information is all that's needed to really say something.


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RE: Testing PPM

this may help,

CHEM-GRO TOMATO FORMULA 4-18-38
GUARANTEED ANALYSIS
Total Nitrogen (N) ............................................................4.00%
Nitrate Nitrogen.................................................................3.50 %
Ammoniacal Nitrogen.........................................................0.50%
Available Phosphoric Acid (P205)....................................18.00%
Soluble Potash (K20)...................................................... 38.00%
Total Magnesium as (Mg)...................................................0.40%
Water Soluble Magnesium as (Mg).....................................0.40%
TRACE ELEMENTS
Boron as (B) ...................................................................... 0.20%
Copper as (Cu).................................................................. 0.05%
Iron (Chelated) as (Fe).. .....................................................0.40%
Total Manganese as (Mn)....................................................0.20%
Soluble Manganese as (Mn) ...............................................0.20%
Molybdenum as (Mo) .........................................................0.01%
Zinc as (Zn)...................................................................... ...0.05%
Chlorine as (Cl), not more than........................................... 2.00%

Note: the iron is DTPA :)

This post was edited by hex2006 on Tue, Apr 1, 14 at 14:16


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RE: Testing PPM

Looks like low octane, high performance inorganic poop to me, Thanks hex ;-). (I know the guarantee of this particular recipe).

Rather than virtually mixing this up it would be practical to hear what was done:

grams each of:

1. grams pure 4-18-38
2. grams pure ag calcium nitrate
3. grams pure magnesium sulfate

4. gallons (or liters) of working solution
5. EC (or ppm @500) of the water alone
6. EC (or ppm @500) of the final nutrient solution including the water.

I think uncertainties over a $10 conductivity 'ppm' tester (including shipping from China), the claimed ppm and EC of the manufacturer and the confirmation of what was actually done and how precisely it was weighed and diluted. If the OP would like an unambiguous answer from someone who doesn't mind looking at it, all that is necessary is to know the 6 numbers above...

OP, Back to your original question if you believe your calibration is 500, the one on the bag is @ 750., so it would be easier just to say the for EC of 1.6 (the first mixture), the ppm on the sac for your purposes is (800 ppm + source water) for the first mixture. That of course depends on the EC being right LOL.


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RE: Testing PPM

I use a scale in grams at work that measures out to the
10,000th of a gram..
I used 2.4000 , 2.4000, 1.2000 and 1 gallon of water..
my PPM on "MY" meter read 1130, thats with a 145 source water.. according to CHEM GROW, it should read 1500 plus source water...

I'm just gonna not worry about the PPM, worry more about PH because right now, My Pepper experiment and Tomatoe experiment look really heathly.. Just trying to get some More Insight into the whole Meter - PPM, etc etc crap.. Everywhere I look Optimum NUTES and PH are all different....So I'm gonna just try and stay within a certain range and call it good..
Thanks for all the Info...


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RE: Testing PPM

My experiments


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RE: Testing PPM

better


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RE: Testing PPM

ppm`s are just a guide, keeping an eye on the daily differences and direction of change (up/down) of the nute ppm/PH will give you a pretty good idea of whats happening and what (if any) adjustments may be necessary.


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RE: Testing PPM

I looked at mix and came up with an 1.68>EC>1.48 based on info I use dicking around with my own recipes. So I would say the EC = 1.6 is probably close enough, which is the claim on the label, but personally put closer to EC = 1.5 mS/cm.

If you want to use your meter as the primary tester then, "ppm numbers" are calibrated to:

145 ppm H2O source
985 ppm fertilizers (all)
1130 ppm EC of working solution

As already mentioned by others, ppm is not straightforward as a quantitative measure if you are just monitoring the evolution of nutrient strength with a conductance tester. But if you get reproducable results you can just use it in that way and control your nutrient strength based on your tester.

When you learn more about EC, the conversion factor for this fresh, uneaten solution based on my 1.5 estimate is that your tester has applied a 660 factor to the EC to display ppm.

So if you just want the EC, for this mixture, based on the assumption of an accurate 'calibration run' above:

Makes your water have an EC about 0.22 and the meter is showing 1130 ppm for what I believe is close to a 1.72 EC working solution. EC = 1.5 ferts. + 0.22 source water.

You can figure out the conversion factor if you want to use 1.6 in the same way, it will be like 6% off.

You can check the calibration by dissolving 3.79 grams of dry table salt (NaCl) into a gallon of water and noting how close it is to 1000 ppm or 1320 ppm.


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RE: Testing PPM

You`ll find the tomato bucket ec will drop much faster than the pepper so be sure to check both buckets individually and adjust as needed. Tomatoes and peppers use the same nute strength and make up initially. The fork in the road comes where the tomato requires more N, Ca and K, if you record the ec/ph daily you`ll be able to see the fork as a fairly abrupt change in the pattern.
Its stuff like this that makes hydro much more interesting than soil :)


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RE: Testing PPM

Ohh.. I did the NaCl here are work last week, and made the 1000ppm solution and believe it or not the PPM Meter read dead Nuts 1000!!!


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RE: Testing PPM

The blue tester I got off eBay was so bad I just kept the batteries as spares!!!


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RE: Testing PPM

Here's the EC/ppm conversion chart

 photo EC_PPMConversionChart.jpg


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