I wouldn't use tap treated with Prime for a reef tank. Bottled water will work. You can also get RO
at most grocery stores now. I used to tote a few 5G containers to Publix every week for water. I think it's like 35 cents per gallon. The best salt mix is the one that works for your tank and budget. IME, Seachem Reef has been great. We also had very good results from Oceanic. Red Sea.... not so much. We've just started trying out Salinity (got a great deal on a 220G bucket). Once the price of it goes to normal, we'll be back on Seachem Reef.