Im just getting all of my equipment together so i can get my grow started and i need a little help on which meter to buy.I already have a digital ph meter and i want to get one to check the ppm.I thought i was supposed to get a EC meter that measures in ppm but all the EC meter on ebay dont measure in that only the TDS meters do.So is the TDS the one i need or am i going to have to shell out alot of cash that i dont have.Thanks for the help