The wording in their directions is a little confusing. What it means is --- if you use a 10ml sample, you multiply the number of drops by 0.5. If you use a 25ml sample, you multiply the number of drops by 0.2. The 25ml sample gives you a little more precise reading, but uses more of the reagents. Using the 10ml sample saves your reagents and gives you a reading that is good enough.

Since you used the 10ml sample and it took 9 drops to clear it, 9 x 0.5 is 4.5 So your FC is 4.5. Then, after adding the R-003, it took only one drop to clear it so your CC is 1 x 0.5 or 0.5.

You were right to take the trichlor tab out. It is adding more cya and yours is already way high. Just use bleach. Since you are fighting an algae bloom, test as many times a day as you can and each time, take your chlorine back up to shock level, which for your pool with cya of 90 will be 20-25. The key to killing algae is to sustain high cl readings without letting it yo-yo up and down.

Regarding adding well water if you do a partial drain and refill, yes, that complicates things. Maybe since it is nearing the end of swim season and you will be draining some when you close the pool for the winter and then adding some water in the spring, maybe just live with the high cya for now and deal with the metals issue in the spring. Any chance you could truck some water in for refilling?

A couple other questions I have:
-- Is this a new pool that was just opened for the first time this year? If so, was it filled from the well?
-- Is your pool green and cloudy or green and clear?
-- Have you recently added any well water?