hanna combo ph/tds is what i use....
my friend got a cheapo ebay one and it worked well,for $10 imo
you can only get the bottom inch wet...but it worked good...
don't get the hanna if you only grow outside....they don't like to sit around for months...
Now that you mention it, I don't think they were cleaning their instruments. They were saying it was inaccurate and having the same readings for everything. Thanks, I'm going to see if my local hydro store carry any Hanna testers.like what? you gotta take care of it or it will become unreliable...
but really,what you hear?