proper mix of chlorine or bleach for water tank

Actually it depends on if you are using a 5% chlorine bleach or a 8.25% chlorine bleach. Both are commonly sold in the store.

But in the end it boils down to this - 100 ppm concentration (of chlorine) for 1 hour contact time or 50 ppm concentration (of chlorine) for 4 hour contact time.

For bleach with a 8.25% concentration (of chlorine) that would mean:
1.5 oz bleach per 10 gal water for 1 hour (100 ppm)
3/4 oz bleach per 10 gal water for 4 hours (50 ppm)

For bleach with 5% chlorine content multiply above numbers by 1.65.