Trying to understand PPM versus EC and how to adjust

[dbrzz]

You need to know what scale your meter uses. View attachment 1227853I have 2 PH and TDS testing devices. The problem is when you look at different manufacturers new trend chart recommendations they sometimes don’t tell you what TDS scale they’re using to measure. One scale is half the other scale. What type of runoff meter do you use?View attachment 1227853View attachment 1227854 PH of the runoff is critical! The pH rising or falling indicates the plant’s uptake of nutrient. If I had to make a choice between buying a pH meter or a TDS meter I would buy the pH meter. The reason for this is whatever fertilizer you use they give you some starting measurements of strength. If you were to simply start at half strength of the recommendation and monitor runoff pH, and you notice the pH dropping or rising this tells you to give More nutrients or less Nutrients. PH drifting upward 6.1 6.2 6.3 give more nutrients, if the pH is drifting down water say you started at 5.9 and it starts drifting5.8,5.7,5.6, Then the nutrient solution is too strong.

 

[PerfecTrader]

You need to know what scale your meter uses. View attachment 1227853I have 2 PH and TDS testing devices. The problem is when you look at different manufacturers new trend chart recommendations they sometimes don’t tell you what TDS scale they’re using to measure. One scale is half the other scale. What type of runoff meter do you use?View attachment 1227853View attachment 1227854

I have that apera pc60. Do you know which scale it uses?

 

[dbrzz]

I have that apera pc60. Do you know which scale it uses?

It actually has both scales on it. So if you want to use the 442 scale which is the NaCl scale, use the salinity scale which is SAL. I would find out what conversion factor your nutrients are using and then you’ll get the actual PPMs or EC recommended.

 

[PerfecTrader]

It actually has both scales on it. So if you want to use the 442 scale which is the NaCl scale, use the salinity scale which is SAL. I would find out what conversion factor your nutrients are using and then you’ll get the actual PPMs or EC recommended.

Roger that and thanks much

 

[phxazcraig]

I'm using one the gives PPM on the 700 scale, and EC on the microsiemen scale. The PPM scale really threw me off. At least the GH charts I have specify a 500 scale for PPM.

 

[Choppr]

Just a month into my first crop with coco and fertigation, and I'm trying to understand the water chemistry better.

One specific question I have is in regards to a feeding chart (Fox Farms hydro chart in this case) that lists desired PPM and EC limits. Doesn't matter what they are in this question.

My chart says PPM in week three should be up to about 1050-1190 ppm, and an EC between 1.5 and 1.7. I'm assuming these are maximum limits.

My question is "Do I adjust to the limit of EC, or PPM, or whichever is higher?" My EC is much higher than PPM. That is, when I finish mixing my nutes I have an EC under 900, but EC at 1.9.

I'm assuming I ignore the PPM reading, and add RO water until I get the EC down to the upper target limit of 1.7.

Here's what I'm doing.

OK, so I start with 10 gallons of RO water, PPM 20 or less. I add my Silica and wait an hour, then cal/mag. I add 2.5ml/gallon, as directed. I note that PPM jumps to 300 at this point.

Next I add my nutes, which for now are Big Bloom and Grow Big Hydro. After the Grow Big, my PPM hits 800 or so and my EC skyrockets to around 1.9 And my pH drops like a stone to about 4.6. I don't think the remaining chemicals change the PPM or EC much.

Next, a dose of Humic Acid (Diamond Nectar), and a sprinkle of Yucca Powder.

At this point my pH is very low and I add some pH UP to bring it up to 6.0 or 6.1. (Once I dump it in the reservoir a Bluelab controller keeps the pH down to 6.0.)

It is at this point that I adjust the EC by adding a gallon or so of RO water. EC drops from 1.9 to 1.7, and PPM goes down to 860 or so. That gives me another 200-300 ppm to play with, but no EC room.

@phxazcraig Nothing worse than chasing your tail my friend - this is another reason I use MegaCrop 2 Part- On their website go to their PPM calculator, it allows you to type in amounts you are using - I mix 5 gal batches for 3rd wk flower I was running 18g PtA and 8g Pt B, the drop down shows you Their Lab Results in Elemental PPM's for my mix above (elemental ppms will always be different than your meter, tds/ec/ppm) I use Hanna model 98129 -
MegaCrop Elemental PPM's = 498.3
My Hanna = 964.2
NPK = 8.2-9-18
what this allows me to do is dial in my Hanna to their LAB values - when a Nutrient Company Provides this its a sell for me - I am also in Coco 60/40 #3 Perlite, High Frequency fertigation. 8 years with MegaCrop its good stuff - Ive been testing Auto's since July of 2019 so Ive had to make some adjustments but I know exactly whats going in, and Calibrate my Meters spot on off their Values- no guessing game- check MC website you might want to make the switch - good luck M8

 

[Moe.Red]

@phxazcraig every meter measures microsiemens and translates that into a number. In the case of a $10 pen, it is just a small chip that puts current thru the probe and translates the analog signal into a digital one that can be displayed on an LCD. Very simple tech, but beware those pens become erratic over time, more so on PH than EC meters.

You kinda blew past @tobh but he was absolutely correct, and he has years of hydro experience. He knows what he is talking about.

Your grow style is even more important on interpreting your chart than genetics. If you have hi respiration rates attributed to things like hi PPFD, CO2, high temps, etc and tend to grow trees you will burn your plants with the numbers the manufacturers recommend.

EC is a starting point only and you won't find optimum recommendations for a strong grower on the back of a bottle.

 

[Moe.Red]

You need to know what scale your meter uses. View attachment 1227853I have 2 PH and TDS testing devices. The problem is when you look at different manufacturers new trend chart recommendations they sometimes don’t tell you what TDS scale they’re using to measure. One scale is half the other scale. What type of runoff meter do you use?View attachment 1227853View attachment 1227854

Gotta love the guy who pulls out the manual!

 

[dbrzz]

Gotta love the guy who pulls out the manual!

Just the facts please no bull

 

[delps8]

The point here is that the CHARTS stating PPM need to state which measurement system is being used. EC is EC, but PPM isn't always PPM. My Foxfarm chart doesn't say which PPM it is, but I see my new GH chart does. I don't know what my meter is set to, but I can guess it's using the 700 scale. It wasn't until this post I even knew there were two scales in use. It seems I have a PPM (700 scale) and a PPM (500 scale) chart.

The more I think about it, the more I wonder why my meter is set to 700 to start with, and if it can be reset to 500..

An EC meter measures the conductivity of the solution. That values is converted to Parts per Million using one of two scales. One scale is the 500 PPM scale, the other is the 700 PPM scale. When you flip the switch to display PPM, the meter just multiplies the EC by the scale (500 or 700).

The 500 PPM scale is commonly used in the US, the 700 PPM scale is more common overseas.

The safest play is to go with the actual reading - electrical conductivity or "EC" - because that's what these devices actually read.

 

[dbrzz]

An EC meter measures the conductivity of the solution. That values is converted to Parts per Million using one of two scales. One scale is the 500 PPM scale, the other is the 700 PPM scale. When you flip the switch to display PPM, the meter just multiplies the EC by the scale (500 or 700).

The 500 PPM scale is commonly used in the US, the 700 PPM scale is more common overseas.

The safest play is to go with the actual reading - electrical conductivity or "EC" - because that's what these devices actually read.

The 700 ppm scale uses the 442 algorithm.

 

[Topsrite]

PH and EC are pretty much the same thing in simple terms. Sounds like youre doing it right. And usually those suggested numbers for PPM/EC are just average every strain is different its up to you to adjust the feed to their needs.

Too many equations, I’m confused. Here’s my question. I have 2 high end meters , one hanna and one Milwaukee. Both read ec close to 2.0, my blue lab reads the same on ec. The thing is that both meters say 1400ppm and the truncheon reads it at 1000ppm. Who’s right? and why the difference?

 

[Topsrite]

Too many equations, I’m confused. Here’s my question. I have 2 high end meters , one hanna and one Milwaukee. Both read ec close to 2.0, my blue lab reads the same on ec. The thing is that both meters say 1400ppm and the truncheon reads it at 1000ppm. Who’s right? and why the difference?

Ok, I re read the delphs8 information and I now understand the us vs euro or non us scale of multiplying at 500 vs 700, but why would they both use the 700 scale for ppm?

 

[delps8]

Ok, I re read the delphs8 information and I now understand the us vs euro or non us scale of multiplying at 500 vs 700, but why would they both use the 700 scale for ppm?

That's how the manufacturers designed their product. Both meters read electrical conductivity of the solution but allow you do display that reading in another format.

From Bluelab (via Google).

"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."

 

[Topsrite]

That's how the manufacturers designed their product. Both meters read electrical conductivity of the solution but allow you do display that reading in another format.

From Bluelab (via Google).

"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."

Excellent information, thank you very much! I love to learn things, primarily science related.

 

[ExNavyInSTL]

I did not read the replies before I gave this answer.

I am a new grower (less than a year, but 4 crops) and when I saw the 500 or 700 conversions for PPM, I ditched it immediately. I stopped letting myself think in terms of PPM and went totally by E.C.

E.C. is universal and the same for everyone on the planet.

In the beginning, I was in the middle of learning so many different things from PAR, PPFD, DLI, and VPD ... for instance. The last thing I wanted was to not get the feeding of nutrients right because of a misunderstanding.