I pre mix my water for at least 24 hours. I use a PH and heater. !st I try to get the temp around the same as my tank. Then I mix the salt, check the salinity and add more salt or water as needed. If you use a PH while premixing, the pH should stabalize, or at least be close. I use instant ocean for my salt. The reason I warm up the water is so the salt dissolves more quickly and I can get a good salinity reading, before I go to bed. Different people use different salt, my LFS
has IO (instant ocean), so ,that's just my supply and demand, but I haven't had any problems. IO dissolves pretty well, but I have to stir it if I put too much in at a time. I don't does either. I did at first because I couldn't get the pH up, but that was beacuse I wasn't using a PH at that time.