I’m not sure why you ordered a hundred dollar meter. The $20 ones we have linked in our list work fine for most people. And even the water proof name brand ones on amazon are only more in the $40-$60 range.
What type of water are you giving it? What is the pH and the EC/TDS of that water?
It looks like you might have a sodium toxicity, which might be from using tap water, depending on what is in your tap water.
It also may very well be just a pH issue, or general nutrient salt toxicity build up in your soil, but we’d still have to get those pH and EC/TDS/PPM numbers to help verify or rule that out.