What meter do you use for your hydro?

I am looking for a meter for my hydro setup, hopeing this will solve some of the plant isues i am haveing...so what do you use?...and what should i look for? I see some out there for 35$ and some for 250$....

I use a generic digital stick, they're about $35, works well.

Truncheon. Reads EC, CF and both .5 and .7 ppm conversions. Simple to use and low maint. Make sure you read on up on how to use an EC/TDS meter properly as well. If you dont know what you are looking at and how TDS meters convert to ppm then you will do more harm than good.

hanna 14.00 bucks ebay