2 quick questions about PAR testing

[cvrle1]

Have some time to figure out height that I will need for my lights, but have 2 basic PAR questions

1) I should set my lights at highest setting I will use during the day (ex: 50% blue, 50% white), and take PAR readings. Correct?
2) Does it make any difference if salt vs fresh water is used? Reason I ask is because tank is on the floor in the garage, and I will move it many more times before it is ready for rocks, sand and saltwater. I dont want to mix saltwater that I will dump after PAR reading are done (dont have anywhere to store it). Waste of 100G of salt and RODI water.

I know I could just wait till tank is setup, but since I have time I wanted to use it to dial in lights as best as possible.

Thanks