Don't waste your money on a
pH meter. Anything decent will cost you about $100 or more, and even if you calibrate and store them properly witch is a big hassle in itself, they can still give you false results. To check pH use the pH drops from general hydroponics. pH drops only cost about $9 and wont give you false results, you don't need to buy calibration fluid for them, you don't need to calibrate and store them properly, and you don't need to buy them batteries. If you do decide to get a
ph meter anyway, make sure you have pH drops as well so you can check to see if the meter is working correctly.