First thing that you should do is order a good test kit. The one we recommend is the Taylor K-2006 or 2006C which you can get through the test kit link in my signature below.

You also should read the Best Guess Chlorine Chart in my signature to learn about the connection between CYA levels and needed chlorine levels.

There is no way to determine how long it will take for chlorine levels to drop, but it is fine to swim with FC at 9. That is within your needed range of 5-10 per the chart.

How high was your chlorine level when you tested pH? Retest it when the chlorine drops back down. If it still that high, then you need to add some muriatic acid to lower it. (Again, read info in sig about using acid safely.) You are right that pools tend to have a pH that they like to be at, but when you retest it, if it really is 8.4, that is too high. You need to keep it between 7.2-7.8.

There is a very handy calculator (in the Forum Q & A section) that you can download to help you figure out doses of things.

Hope this helps. Let us know if you have more questions.

Welcome to the Pool Forum!