Nutrient PPM Question

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infdjedi

Well-Known Member
Hi Folks,

Probably a basic question here... but want to make sure I am doing the correct thing.

My water after RO has like 20 ish PPM. My target PPM for my plants in terms of nutrient & Cal Mag is 700 PPM currently.

When I add Cal Mag to 1 gl of water the PPM goes up from 20 to 100.

Does this mean I add enough Nutrient (GH Maxi Gro / Bloom 50/50) to reach 700 PPM? Meaning.. add 600 PPM nutrient solution?

OR

Do I add 700 PPM nutrients with a final PPM of 800?

I am thinking the first one.. but just double checking... much love.
 
N

Norville Rogers

Member
The first one. If you want 700 ppm you would first subtract your water (20), then in your case Ca (80), and then the remaining 600 is nutes and\or additives. For what it's worth if you're new i assume you are using a meter to get your ppm but should realize ppm on a meter is actually (usually) tds based on the EC and is measuring the conductivity of the nutrients rather than the molecular ppm.
 
I

infdjedi

Well-Known Member
Norville: Thank you. I have lots of soil experience but only one rDWC run under my belt, so I would say I am new.

I use the hanna pH / TDS combo meter. It says it is measuring TDS as parts per million and EC as mS (microsiemens/centimeter). It was my understanding that I can convert the PPM reading into EC quite easily by dividing the value by 500. Ie.. 500 PPM = 1.0 EC. So at 600 PPM I would be at 1.2 EC. I havent been using the mS reading.. but in reading online for the 500 ppm scale you divide by 2.. so a 1200 mS reading is a 600 PPM reading or 1.2 EC reading.

Am I correct here or off base?
 
rkymtnman

rkymtnman

Well-Known Member
are you sure you need cal/mg with the maxi series? most people don't need it even with RO. just a FYI
 
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Norville Rogers

Member
You are right with your understanding and your meter is fine. I use a Bluelab Guardian myself. All i had meant about the meters is that they rely on EC and then convert to tds\ppm with your formula. The problem is the meters are too "dumb" to differentiate what is actually in your mix nutrient wise and only measure the electro conductivity of the nutrients. If you were to change the ratio of the nutrients added it may have a different electro charge when the nutrients react and doesn't properly give you an accurate ppm reading. As an example if i mix up nutrients that equal 500ppm in a nutrient calculator that calculates the molecular pmm when you measure it with your pen it may read 600ppm or 1.2 EC. I hope that made sense.

Edit. Not to highjack, This is for anyone really. I made a nutrient calc where you can enter in the guaranteed analasys for a product and it will display the ppm and you can create profiles with days, gallons, ml a gallon etc. that display the results in a weekly feedchart. The EC needs a handicap each product though i find when using 5ppm RO water. I assume my math is ok and i'm doing it right, but the EC is a p.i.t.a. I was thinking of sharing it but only wanted to if the math seemed proper seeing as i'm a nobody. FWIW here's a few shots to show the difference between actual ppm and EC\TDS. The feedchart i haven't worked out the ratios i want to use yet so it's just p.o.c., i''ve been working on the math side.
 

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amneziaHaze

amneziaHaze

Well-Known Member
when i put in my hesi pk ppm doesnt change at all but there is huge amounts in it soo you have to remember how much you put in because the meter doesnt tell you
 
amneziaHaze

amneziaHaze

Well-Known Member
in 10 liters if i put more than 10ml i will burn plants but that 10ml will not show on the meter. okej i have the cheapest one but i know they read electrical conductivity
 
P

Psylo

Member
It doesn't make sense that it will burn the plants but not show on the TDS meter, as others have said your meter may be off.

Also that 10ml in 10L can burn sounds crazy concentrated, at least compared to what I am mixing.

I normally aim for about 1.6 EC total in my DWC, never had nute burn problems around that.
 
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amneziaHaze

amneziaHaze

Well-Known Member
Some stuff is more conductive than others.soo tester doesnt register same. He doesnt know whats inside it just checks how much electricity can go in the water.
Its not just 10ml i add it as booster with my regular nutrients sorry for that
 
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Norville Rogers

Member
I have the same problem with meters sometimes not reading any EC, do you happen to use RO water? It's strange how my readings show up sometimes. In my scenario i have 3 meters:
1-Bluelab Guardian, 2-Bluelab Combo meter, 3-HM Digital TDS
For a hypothetical example, i'll have 5 ppm RO that meters 1 & 2 shows zero and the HM shows 5 ppm
-i add ie: 2ml a gallon of Pro-Tek and 1 reads zero still, 2 reads 50, and 3 reads 44.
-i add a few hundred ppm of nutes like Jacks and meter 1 reads 650, 2 reads 600, and 3 reads 632.

I attribute it to RO, the silica, and Blulabs less than stellar EC probes. The bluelabs always read the same ph and are calibrated and less than a year old. I go by the HM numbers for testing and reference.
 
ThrowMeOut

ThrowMeOut

Member
@Norville Rogers
Hey there, I know it's been a few months and this thread is kind of dead but I was wondering if you ever figured out the math on accurately calculating EC from a product label?
And if you were perhaps willing to share your results? I've been working for a few months on doing something similar, feel pretty confident in my math for the actual elemental PPM of a nutrient schedule but can't get a grasp on converting that to a number consistently similar with measured EC of a product
 
N

Norville Rogers

Member
I know what you mean regarding the calculations. I'm by no means an expert but have read enough to at least get thew real ppm right, but as far as the EC there are alot of variables and i can't find a standardized way i'm comfortable with unless you calculate each product yourself and add a multiplier that averages out a larger ppm guess. The problem is the different elements have a different electrical charge, but it also depends on the amounts used in comparison to other elements and also your starting waters ppm and makeup. I use RO so i'm not sure if it effects my results, but if i take 1 gram or ml of a product and add it to a gallon and measure the EC\TDS i can then compare it to the real ppm with the spreadsheet and create my multiplier. After doing that for each product if i was to mix lets say Jacks 321 it would give me the ppm, tds and EC and is is alarmingly accurate to what the final reading on my meter is, lets say 20 tds off from a guess of 849 tds. I look at the real ppm but use the tds as my guage for if the plant is eating and what base number they are usually comfortable with. Hydrobuddy (i think) uses an EC multiplier like i do but they do it for each element rather than each product. I have the ability to do this in my spreadsheet but find it's not as accurate as on a per product basis because of the specific chemical compounds used in the fertilizer. Things like calcium have ridiculously high readings for me and i find if i try to tweak just that element then the accuracy doesn't carry over well enough each product. It's one of the reason i made mine. Here's an example of Jacks, look at the 7th column to see an example of the multipliers i used. 18 columns over and 2 down you can see where i can incorporate an element multiplier, if you have a number for me to try i can throw it in and take a look.
 

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ThrowMeOut

ThrowMeOut

Member
Norville Rogers said:
I know what you mean regarding the calculations. I'm by no means an expert but have read enough to at least get thew real ppm right, but as far as the EC there are alot of variables and i can't find a standardized way i'm comfortable with unless you calculate each product yourself and add a multiplier that averages out a larger ppm guess. The problem is the different elements have a different electrical charge, but it also depends on the amounts used in comparison to other elements and also your starting waters ppm and makeup. I use RO so i'm not sure if it effects my results, but if i take 1 gram or ml of a product and add it to a gallon and measure the EC\TDS i can then compare it to the real ppm with the spreadsheet and create my multiplier. After doing that for each product if i was to mix lets say Jacks 321 it would give me the ppm, tds and EC and is is alarmingly accurate to what the final reading on my meter is, lets say 20 tds off from a guess of 849 tds. I look at the real ppm but use the tds as my guage for if the plant is eating and what base number they are usually comfortable with. Hydrobuddy (i think) uses an EC multiplier like i do but they do it for each element rather than each product. I have the ability to do this in my spreadsheet but find it's not as accurate as on a per product basis because of the specific chemical compounds used in the fertilizer. Things like calcium have ridiculously high readings for me and i find if i try to tweak just that element then the accuracy doesn't carry over well enough each product. It's one of the reason i made mine. Here's an example of Jacks, look at the 7th column to see an example of the multipliers i used. 18 columns over and 2 down you can see where i can incorporate an element multiplier, if you have a number for me to try i can throw it in and take a look.
Click to expand...
I think Hydrobuddy changed their system a little bit back to use a different formula now to calculate things rather than using static multipliers, apparently it works better but the math is honestly quite a bit above my head.
Ca does seem to be a bit of a beast to accurately predict, it interacts with just about everything and really skews things. I've also found that unless you're working with straight salts, nutrient products often have stabilizers in them that can mess with the EC readings a bit.
I'm pretty well in the same boat though, I feel fine with the PPM calculations but EC just doesn't quite work right and I don't think there's enough consistency in the numbers (that I get at least) to really nail down a standardized method
 
PJ Diaz

PJ Diaz

Well-Known Member
ThrowMeOut said:
@Norville Rogers
Hey there, I know it's been a few months and this thread is kind of dead but I was wondering if you ever figured out the math on accurately calculating EC from a product label?
And if you were perhaps willing to share your results? I've been working for a few months on doing something similar, feel pretty confident in my math for the actual elemental PPM of a nutrient schedule but can't get a grasp on converting that to a number consistently similar with measured EC of a product
Click to expand...
See the attached pdf.
 

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Norville Rogers

Member
From what i remeber last i looked, is that they take into account more variables than i do where they have a somewhat static number that becomes dynamic depending on what your water chemistry, ammounts used of the particular element, and wich compounds were making up the solution. So for 200 ppm of Ca it would figure out the ppm, and then use a few variables to average out what it thinks the ec would be. I think the variables were wich substance it came from (ie: calnit) that may have other substances in it, the amount used overall compared to other elements, and how you calibrated the static number for the element, i think using sulfur as their base (is "neutral" EC?). Although my method is a little barbaric, most people use less than ten products so if you only need to adjust and measure 10 gallons worth of testing to make life easier until you change brands then i'm not sure this hobby is made for them haha. I agree when you mention the stabilizers, using RO water i've looked into bicarbonates to add back hardness (decided not to) and think the ones found in tap and ferts will mess with the readings, and possibly only takes 1 product out of 10 to do it. My spreadsheet (to me) is useful to know what ppm you are using in an already established feed regimen, and then fill in the blanks with what you need vs what you use, like adding MKP and staying below your ppm threshold.

@PJ Diaz that's useful but not in this context. Hydrobuddy is what would use that (or your products lineup); what we are talking about is more along the lines of taking those results and messing with them because we think we can do better.
 
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