TDS Calibration

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illbeyourhuckleberry

Member
Hi, ive posted this under another topic but noone seems to know the answer so i will ask again here. I've recently purchased an Oakton EcoTestr TDS meter and first thing I did was to calibrate it with the Hanna HI 70442 1500ppm packet I was given at the store. I am concerned that since it does not specify on the packet weather it is suppose to read 1500 on a .5 or .7 conversion that I may have screwed up my meter readings. Right now (after the calibration) my tap is reading @ 200-210, my Lucas formula for Floros (5/10) is reading @ 1160, and my Lucas formula for HIDs (8/16) is reading 1560, and just for kicks I mixed up the "aggressive vegetative growth"formula as indicated on the chart on the bottles of GHFlora series (2-3-1 tsp/ga) and tested it with the meter and it reads out of range, so it must be over the testers limit of 1990ppms. If you have any info that might help or you think the numbers above sound about right please let me know, i'd greatly appreciate it - thanks
 
EvlMunkee

EvlMunkee

Well-Known Member
Hanna uses a .5 conversion.
I don't know about levels of Lucas products. 200 ppm sounds reasonable for tap water. Do you know what it was before you calc'd it?
 
EvlMunkee

EvlMunkee

Well-Known Member
asaph said:
i dunno why you americans don't just use an EC meter...
Click to expand...
I agree. Whenever the conversation comes up you have to know the conversion factor. Much simpler to use EC.
It's crazy the way there are 3 different factors depending on whose shit you buy.:peace:
 
I

illbeyourhuckleberry

Member
I am definitely the newb here but are you all sure about the Hanna Solution being .5 conversion? The reason I ask is because I have read that a 442 conversion uses the .7 rate and that the NaCi conversion is .5 That said I would think that the number on the Hanna Solution which is labeled 1500ppm (HI 70442) is refering to the 7.0/442 conversion factor. This is the info I came across, please let me know if you think I am misinterpreting it.

The problem is lack of consistency among manufacturers when it comes to conversion factors. This is where it may get a little confusing. Most meter manufacturers in the hydroponics industry use one of two conversions. There is the 442 conversion (40% sodium sulfate, 40% sodium bicarbonate, and 20% sodium chloride) which some say is the closest thing to a hydroponic solution. The 442 conversion is approximately 700 x EC in millisiemens (mS). Then there is the NaCl conversion (sodium chloride) which others say is the closest thing to a hydroponic solution. The NaCl conversion is approximately 500 x EC in millisiemens (mS). You can see where the confusion comes from because the same solution will read 2100 ppm on one meter and it will read 1500 ppm on the other. That is a difference of 600 ppm which as many of you know could be devastating. Both meters are functioning correctly they are just calculating the TDS using a different formula. So, if you do not calibrate your meter using the correct calibration solution your meter could give you a very inaccurate reading.
The solution is simple, use EC. With EC, no conversion is required so all meters will read the same regardless of the manufacturer. Here is a chart showing some sample measurements:
Electrical Conductivity (EC)
Parts Per Million (PPM) millisiemens (mS) microsiemens (µS)
NaCl Conversion 442 Conversion 1.0 1000 = 500 ppm 700 ppm 1.5 1500 = 750 ppm 1050 ppm 2.0 2000 = 1000 ppm 1400 ppm 2.5 2500 = 1250 ppm 1750 ppm 3.0 3000 = 1500 ppm 2100 ppm​
 
EvlMunkee

EvlMunkee

Well-Known Member
I'm glad you challenged me on that. I have learned a little more.
Hanna apparently makes both factors and both solutions. The solutions are 7032(@.5) and 70442(@.7)
I use the 7032 for my Hanna 981504/5 meter. So if the Oakton converts @ .7 it would use the 70442 solution.
I didn't mean to misinform....my bad:?
 
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