This is a rather simple sounding response. What I do is: have a RO water change tank and know exactly how much you will add to it to make 1.025. You can draw a line with a sharpie marker on the tank and have a container or scoop used to add the same each time. It really makes guessing the mix much easier. But of course with out a doubt, with out a doubt, this must be important since I repeated it. USE A REFRACTOMETER, THERE IS A REAL DIFFERENCE, BEFORE ADDING THE WATER TO YOUR SYSTEM.
I would also use a ca test prior to adding water also, Instant Ocean when I make it up needs some ca flakes, and baking soda. I think when I used tropic marin I got more algae on the glass of the tank from slightly more phosphate in the mix. This may not be true but I think there is more phosphate in TM.
Good luck!
Ed Ralff