I've used tri-meters. I do not recommend them. I have also used the bluelab monitors and I had to return that because it would not stay calibrated for more than a day. Then I used the black Hanna combo pen with EC/PH/TDS and I found it to be the most reliable and accurate. I have two of them.
HANNA PEN COMBO pH/EC/TDS TESTER HI98129
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I used the same pen, it has worked very well for me for over a year.
For me, a absolute must is a good shot glass to store the pen in. Just fill the shot glass about 1/3 full of 7.0 buffer solution and bamm your good to go.