The abridged version is the higher your CYA reading the more chlorine you have to add to "sanitize" the pool. Which is why pucks/sticks aren't recommended on this forum because the longer you use them the more CYA is added to your pool (even though the ingredients on them don't come right out and say they have CYA in them, when they say "dichlor" or "trichlor", then they have CYA in them) and the higher you have to keep your chlorine level just to kill the normal everyday stuff that's in the pool.

Since you have no CYA, then you need less chlorine to do the job. I would suggest putting some CYA in your pool though...start out with just a little...enough to get about 20 PPM. I don't remember how many gallons your pool is, but doing reverse calculations from you saying BleachCalc said 2.5 gallons for 10 PPM, then I'm guessing 15,000 gallons. There is a Cyanuric Acid calculator in the BleachCalc, so use the amount it says when you plug in your gallons and 20 PPM. Easiest way is to put the amount it says in a sock, tie a knot in the top and hang it in front of your return jet. That way if you have to backwash during the time it's disolving (it can take a week or so to dissolve) then you're not washing it out of the filter. If you pour it in through the skimmer then you can't backwash for at least a week or else you're rinsing the undisolved granuals right out of the filter.

Depending on the size of your pool, you should be able to retest around a half hour (smaller pool) or an hour for chlorine. I'd wait a week to test for CYA.