Leaving your water out for any number of days will do nothing to reduce the TDS (Total Dissolved Solids.) As for living in NJ, just wait, having just decriminalized the market will expand very rapidly and you won't have to order from the internet anymore. Did you purchase calibration fluid for the tester? If the tester is properly calibrated then you have just found out what is causing your burned leaf tips. pH is very important, even in soil. It controls how available any nutrients, when present, are to your plants.
The pH scale represents the acid to alkaline balance of any fluid, 1 being completely acidic and 14 being completely alkaline, each number indicating a ten-fold increase in alkalinity. The suggested range for growing cannabis in soil is between 6.5 and 7; this means that your water, if truly at 8.7, is 100 times more alkaline than suggested. As you get to a pH over 8.0 your plants start to lose the ability to absorb important nutrients such as nitrogen and phosphorous, while also allowing excessive absorption of ammonium. With your pH so basic, not allowing absorption of the two main vegetative nutrients, you just compound the chances of toxic salt buildup already present due to hard water. Once again my solution is to begin using R/O water, as pure water is always at a pH of 7.0, and R/O water is very close to pure.
It seems that every possible cause of the problem that you are currently having can be solved by improving your water source. Thank you for the invaluable experience gained wile teaching.
-GNS