Are these the same things or do they each measure something different? DO i need both? I know it measures PPM and electric current but need to know the difference. I have read a little bit on them and needed someone to clear it up so i can understand it better if they can.
The only accurate way to know your Total Dissolved Solids in a nutrient sample is to evaporate the water in a known quantity and weigh what is left. And you would need a lab to do this. It is known that measuring electrical resistance in liquids can give a relative value that comes close to the TDS value. The problem is not everything we put in our nutrient solution has the same resistance. This is why not everyone will use the same conversion formula. So there is no such thing as a real TDS meter. Just EC meters that multiply EC by .5 or .7. The answer will be in parts per million on most meters. Below is an explanation I got from one of the retail EC meters websites: Electrical conductivity (EC) is measured in microsiemens per centimeter or µS and is used to estimate the amount of total dissolved solids/salts (TDS), or the total amount of dissolved ions in the water. People try to convert this value to parts per million by multiplying the EC value by .5 thru .9. Most use .7 to get the estimated PPM from an EC value. I just use the EC value because it will be about the same from person to person. But alot of tables for feeding are in PPM so you have to convert your reading. Most meters will let you adjust the PPM value by .5 or.7 I could be all wrong about this (happens alot). R.
Very clear ty. But like every good answer comes another question and yes it is and ebb and flow system. It sounds like there is a lot of variance to these meters. If they are not accurate is it worth the purchase? I will not be adding a lot to my water just the minimum nutes required. So they could be close to the same eletrical resistance. I will probably still buy one because it is only the best for my baby. Ebay you can get a digital ph meter and an EC meter for about $50-60 bucks. If you get them both at the same place and the same time you will save on S&H, saving another couple $$. Ty