TDS meter

I have not used a TDS meter once, basically because I don't understand the concept. Seems to be the only part of growing that I'm still completely oblivious to. Can someone share with me the point of measuring ppm's, expecially when using nutes? Thank you

essentially... ppm's are a measurement of dissolved solids/minerals in your nutrient solution. If you test your water before you add nutes you should have a ppm reading around 75-100ppm, add some nutes and the ppm will go up, for example.

ppm's are very important when growing hydro... in soil you have a better buffer

If ppm's are out of wack, what is the consequence? Is there a way to raise ppm's or lower them?

You can raise or lower ppm's by adding plain water to lower, add more nutes to raise... If you're ppm's are wicked high, your feed solution is gonna be strong and you will run the risk of nute burn. If your ppm's are way too low then you run the risk of your plants not getting enough nutrients and having them lack something.

Depending on what nutes you use... when I used to do hydro... I'd usually have the feed solution in my reservoir at around 1500-1700ppm. Thats not a hard and fast rule and I'm assuming every nutrient has different ppm values.