Ppm in this scenario means for example if you're using ro water ( because it's TDs is 0 so it's easier to explain) means anything added to this ro water will increase its total dissolved solids. So for example. If you add ferts to your water it will raise your tds. This way you know exactly how much fert you are putting in and then how much the plant is using. So now let's go with this seniero. You test your tap water or whatever your using for your plants. Test that with your tds meter so you know where you are starting. Then when you add your ferts to the water test it again and subtract the number of your plain water before ferts and you will know exactly how many ppm of ferts you are using. In my opinion a TDs meter is much more important for running hydroponics. That way you can tell how much ferts your plants are using in a given day and you know exactly how much ferts to add to your mix so you always know when to add more ferts. With ppm you can dial in your ferts better then just going with ( add a tablespoon per gallon of water. I hope I didn't confuse you with my explanation. You will need 2 different types of calibration liquids to get your tester working and it's also recommended to have a storage solution for when your not using them. Or they will not last long. If you let the probes dry out to much they will malfunction and not work right. I know it's a pain in the ass but that's the way it is. I found that out the hard way years ago. Some people use to water for storage. I can't verify this because when mine went bad years ago I just broke down and bought the real storage solution because I didn't want to take the chance of ruining another device.
Not at all, I grew for a few years and kept myself and my wife in smoke all year long. But when I dialed in my ph the same plants produced more, faster. For me the TDs meter is less important because I am growing in dirt not hydro. But every now and then I will test runoff when plain watering so I can see how much ppm is coming out. If it's life I will back off the ferts a little. No point in wasting ferts. Those cost mucho denerio. If I see not much comming out I will increase a little. Every plant has a sweet spot. The closer you can get to that sweet spot the better the plant does. So if you can get your plant to grow faster and produce more the better for you. jmo.
