In hydro you ph is a little high you should be closer to 5.2 to 5.8 but 6.0 is ok later in the life cycle but not early on.

Water temp in the of 72f - 73f is a little warm but not that far out of range. The problem is when it goes higher at times you don't check it.

You did not answer the water question of what type of water you use. I will assume you are using local city water. The challenge to growing in hydro with out having the proper meter (I understand about working your ass off) you not only need a quality Ph meter with calibration solution you also need a quality TDS/EC meter as well. You may want to try buying online from a shop or eBay if you can.

Your water schedule sounds fine but I can only guess what the problem is with that one at this point.

What is your grow medium?
Are you using Rockwool? Anything with it?

Your water may be to hard to start with, you can't be sure with out a TDS/EC meter.

You may at worst just need to cut a clone and hope you can get a few to root. This one may not make it so be prepared just in case. You can call this one a learning experience. We all killed one or two in the beginning so don't give up.