First time using TF-100

Hello! I am a first-time pool owner, and I recently bought a tf-100 test kit and downloaded the poolmath app. We had a pool guy the last four months but since we just emptied and refilled the pool, we decided it would be a good time to start doing the maintenance ourselves. These are the results I got:

FC: 5
TA: 85 (took it twice and got 90 and 80).
CYA: 20
pH: having a hard time reading the block, it is somewhere between 7.5 and 7.8.
CH: 325

I have a few questions:
Poolmath gives me a...

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