Leanne, you still haven't told us what product you are using that I have read. This is important as different products are different concentrations (particularly liquid supplements. What test kit are you using? Dosing is simple if you give us the right information!
Do this:
1) Test alkalinity. Record.
2) Add 3 tsp of DRY sodium bicarbonate alkalinity powder into about 2 cups of RO water. Mix well, pour slowly into the sump (take about 30 seconds to pour).
3) Wait an hour. Retest. Record.
Post back with your results.