Looks like you'll need CYA, muriatic or dry acid ( dry acid is easier to deal with, but more expensive and less effective than muriatic), and bleach. The pH wont go down because the water is circulating--if anything it will go up.

Add bleach to getthe water to around 3-5 ppm, and you cango ahead and add your cya. Follow label dose for a target of 20 ppm, but only add about 2/3 of the dose. Dont backwash or test for it for about a week, and keep in mind uou'll have to bleach daily until cya is in the pool.

Janet