You can use the pool while you are working on lowering the alk. You won't want to drop your pH too low --- probably just to about 7.0 and then you start aerating it back up. It is fine to swim with pH at this level. A fountain is certainly one good way to aerate in addition to aiming the return jet upward to create a lot of bubbling and splashing on the water's surface.

You add acid again when you aerate your pH back up to 7.8 or so. Then, it is time for another dose of acid. Adding the acid drops the ph and the alk level. The aeration brings the pH back up without the alk rising. It is a ratcheting process and works great but it takes several cycles, especially when your alk is very high as yours is. It is not the aeration that drops the alk. it is the acid. The aeration brings the pH back up so that you can repeat the process.

To clarify for you, this does not affect the calcium hardness. It affects the total alkalinity which is not the same thing. One thing at a time. Once your alk is where you want it (and 100 is a good target) then you can see about lowering the calcium hardness. Ask about that later.

Regarding doses ------ the pool calculator is complicated. One that most people do better with is this one called the 'bleach calculator.' But, it has way more calcs than just one for bleach. If you click in the upper left hand corner, you'll find many more. After you have a look at it, let us know if you still need help figuring out doses and we'll be gad to help.

http://www.poolforum.com/zxq/BleachCalc262.exe

You're doing great!