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

 

[mike550]

@cvrle1 Not a lighting expert by any measure but here are my thoughts.

The optical properties of salt vs fresh are probably close enough for what we do. If anything as the tank gets more particles in the water column that might affect your readings later — but I really doubt it will be meaningful.

As to how to calibrate, I started with a goal of having around 100 PAR on my sandbed during my “max“ lighting period, and set my lights accordingly. Then I just measured various spots on my rockwork and mapped it out. I suppose if you know the types of coral you plan to have then maybe adjust your lights to your goals.