Just buy a rodi system, they are not that expensive and worth every penny spent. Test PO4 as well. Tap water is BAD for saltwater and reef aquairum use. API are junk but give you a general idea, I know I have used them for years. You dont need to worry about test ammonia and nitrite once the tank is cycled unless there is a major issue like lots of die off. Nitrate, po4, alk, cal, and mag are more important to test regularly. Get some better quality tests kits like the Red Sea ones or Salifert. Hanna checkers are nice too. More flow will help if you dont have a lot, you want way more than you think. If you sand is not almost getting blown around you need more flow. Regular weekly or bi weekly water changes will help with nutrient control and the algae, onlybuse 0 tds rodi to mix new saltwater. What size tank is it and do you hqve a skimmer?
Since you requested my water test results here they are from Monday, and stays very stable.
Ph 8.1
Salinity 1.024/34.5
Temp 77.8
Alk 9 dkh
Cal 400 ppm
No3 0 ppm
Po4 >.25 ppm
All test but temp and Ph and salinity are done with API Reef Master kit. Ph and temp tested with Reef Keeper and probes calibrated 3 months ago.