In almost all cases, good aeration after adding a salt mix will bring the pH up to the proper levels. Buffers are a poor way to raise the pH since you raise the alkalinity substantially for a relatively small pH increase. Good aeration with fresh air will make a big difference, if necessary.
Fishieperson, it is good that the levels are low, but chances are, they are high enough to cause issues. Algae doesn't need detectable levels to have plenty of phosphate to grow. Unless you want to fight the problem long after you eventually get RO/DI water, then go ahead with tap. It would be easier and cheaper in the long run to simply get the RO/DI unit and make your own water. It will save you a lot of time and frustration in the future, as well. FWIW, good units can be had for ~$150-$180 USD and will be all you need to have good quality water.