PPM meters vary a lot in quality. anything Hanna is pretty much gonna be good. I use that PPM meter from the Zero Water, that they give for free, and it actually works really good. here is a link for a cheap hanna, but this is their cheapest one. Hanna Instruments: HANNA PRIMO TDS TESTER [716833] - Timers & Instruments - Discount Specialty Farm, Greenhouse & Garden Supply Store - Horticulture Source. I cant recommend it since I haven't used it, but really, you cant go wrong spending like 50$ more for a decent one. I have read that they all pretty much start off accurately, but the cheap ones become inaccurate more rapidly than more expensive one. Infact, many have calibration modes used with calibration liquid you can buy. The main thing is, always keep the electric diodes clean, the part that goes in the water, either by blowing it dry or wiping off. This ensures long lasting accuracy