The tds meter i got with my hydro set, dosent seem accurate at all, dose anyone have any suggestions on meters they've worked with and work good for under $50?
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The tds meter i got with my hydro set, dosent seem accurate at all, dose anyone have any suggestions on meters they've worked with and work good for under $50?
Search the eeee-bay for 'oakton tds'.
Go to your hydro store and get one of the premixed TDS calibration solutions from GH. Comes in a small foil packet that looks like a big ketchup packet. Should cost about $1.50.
Dip your pen in that and see if your pen is not accurate first of all. TDS is SO simple its very hard to go wrong. Then if its off and cannot be calibrated or won't hold calibration then get yourself a HM Digital meter. About $40 and use EC from now on. TDS is not accurate to begin with.
TDS is only the type of measurement and measures the same thing as does EC. TDS is indeed as accurate as EC, if not more so (considering it typically has more significant figures per readout). As long as you set the correct conversion ratio, TDS is fine.Quote:
Originally Posted by herbie the love bud
Can't agree with you G. First of all, TDS, Total Dissolved Solids, is something no meter actually measures. Instead it uses EC, Electrical Conductivity, to guestimate for you what the TDS is based upon a theory that the TDS effects conductivity in water.Quote:
Originally Posted by gainesvillegreen
OK, next the TDS is actually just a factor of EC in microsiemens times 600 - 700. Each pen manufacturer uses a slightly different factor and some nute companies put out a different TDS chart per popular meter (Hanna, GH, etc...).
Took me a while to get my head around, but EC is the true reading (so to speak, as there are other factors) and TDS is kind of the educated guestimate.
Yep, you are right about that, but EC meters do generally give you an approximate TDS reading within 10% accuracy, although that's not great, it's the best your gonna get unless you do gravimetric analysis. But I go by EC myself anyways.Quote:
Originally Posted by herbie the love bud
First off, the biggest reason why people use TDS instead of EC is because it is what more nutrient companies use. Because most nutrient levels are recommended in TDS, it only makes sense to measure the same.Quote:
Originally Posted by herbie the love bud
I guess I'll split the difference with you. While TDS is indeed a number generated from an EC reading using variable conversion rates, they're both still about the same and shouldn't vary by more than 10% at under 2000ppm.
EC is not an accurate measurement of TDS, so neither is TDS when converted from EC. EC is a much more temperamental reading for nutrient levels than one might think. Given two solutions with the same TDS levels, but different chemical composition, the EC reading can vary significantly (depending on the size of the ions and their charges). So if you have your vegetative and bloom nutrients, both with the same actual TDS concentration, the EC will vary between the two because of the different salt concentrations in each. Basically, each is as good as the other because your choices are an inaccurate number, or an inaccurate number based upon an inaccurate number.
I'd like to know what this 'theory that the TDS effects conductivity in water' is all about (unless I misread you). Theory? no. Water is a piss-poor conductor of electricity, period. The ions in the water are what allows the water to better conduct electricity.
I would hardly call the conversion from EC to TDS a 'guesstimate'. The conversion runs from about .5-.8 depending on the concentration. The whole reason that the conversion is dynamic, rather than static, is specifically to remain more accurate. For agricultural usage (which is why we're here), the most accurate conversion would be right in between the 600-700 you listed. There should be no more than a 10% variance between the two at this conversion.