Hello,
My english isn't good enough to answer on all questions correctly.
If you don't become a right answer by me...please take a look at my website, where you find 90% of your answers in english.
No Mercy Supply
Since I'm a Dutch guy who's 53....My english is totally poor.
And YES....shure you need your EC meter !
The Tensiometer only tells you when and how much water you should give your plants.
Stay cool,