At this point you should need to make more salt water, you should only be adding fw
to the tank as the level drops. Salinity will rise as water evaporates,to lower salinity you need to add fw
Simple trick: mark the side of the tank at full water level then remove one gallon (may need to mark smaller increments) and mark that level. Now add the sw
back into the tank. Keep a bottle of fw
near by and every day or so add the fw
to bring it back to appropriate level. the closer you keep the water level to full the less salinity will vary.
pH is a related but separate issue. Related in that the water you add has ions in it which affect the pH. Best solution is to use deionized water usually made or bought as ro
water. using deionized water will make the pH will more stable. You may be able to get ro
water from supermarket or walmart, i get mine from whole food. Second choice is to add buffer to water like seachem marine buffer or reef buffer.
There is still some equipment that you need before you add livestock. Your going to need a protein skimmer.