This is actually my second attempt at this since my first one didn't work so well. My first attempt failed because of an improper connection made on the second (unused) op-amp on the LM358.
I first had the unused op-amp with one input to GND and the output feed back into the other input like this:
That didn't work and actually made the IC extremely hot and readings fluctuated erratically. I gave up after that failed try, but after a month or so the topic came up and a few members helped me out. It seems that a dual op-amp IC like the LM358 won't work correctly since both op-amps feed from the same power supply, but would work with a single op-amp IC.