Fill it with tap water first to do a leak test.. then drain it back out.
I'd wait till you get the
LR, because you want it to sit on the bottom of the tank. either that or build a
PVC skeleton of some sort to hold it up and put THAT on the bottom
you can get started mixing water though. I'd fill the tank about 70%, add the right amount of salt mix, and put in a
PH to mix it up. That way when the
LR shows up, it will be ready to go in the tank