I collect my RO water in a 5 gallon bucket. Since you must only use cold water with RO units (to protect the RO membrane) I usually drop a small heater in the bucket once it's full to warm the water to tank specs. I also drop in a water pump to circulate the water to speed heating and also to help with mixing the reconstituting powders.

I then add 1.5 tsp of Seachem Equilibrium to increase the GH (you would be adding Barr Booster in your case, probably different amounts also) and .5tsp of plain baking soda to increase the alkalinity (KH). I add a few drops of Seachem Prime just to be sure all chlorine/chloramine is neutralize (since I don't keep up with how long I've been using my carbon stage filters).

Last time I checked, this puts my GH around 6 and my KH around 5, or maybe the other way around. Remember, this RO water is starting out with a GH=0 and KH=0. Anyway, I works well for my plants and fish so I've never felt a need to adjust it. I dunno what my PH is because I use aquasoil and blast Co2 so my in-tank PH is always on the low side, I never test. Back when I did test seems like it was in the 6.x range is all I remember. I don't even have any test tubes left..broke them all and never replaced them. Math/observation is more trustworthy anyway.

The baking soda to increase KH is what's going to affect your PH the most. The less KH you add, the lower your PH will be (since you aren't using Co2 which lowers PH). If the aren't adding Co2, you don't need the high KH to buffer your water against a PH crash.