feetr2c said:

10 - 2.0 = 8 ; 8 / 10 = 80% loss? Can't be. And in your above example, 6 is more than half of 10.5, so therefore your loss is over 50%.

Yes, the above example would be an 80% loss.

If FC = 10 and then went to 2, that would be a loss of 8, or a 80% reduction. the ending number (2) is 20% of 10.

*

*The above example would also send me into a full-out algae panic, causing me to lose 80% of my chlorine inventory *
feetr2c said:

It should be:

(10. 5 / 18.5) * 100 = 56.76% loss for his night reading and,

(6 / 10.5) * 100 = 57.14% loss for his day reading.

You are dividing the ending FC number by the original FC number, which is not the amount

**lost**. You formula is determining the current level of chlorine (in percentage), assuming the high number (18.5) is the max and 0 is the low (which is why your number + my number = 100%).

Look at the first example; The original FC was 18.5. Just to make things simple, 50% loss (half) would mean the ending test would show 9.25 FC (18.5/2). Any number larger than half would be a percentage loss less than 50% - any number less than 9.25 would be a larger loss than 50%. He went from 18.5 to 10.5, which meant he lost

*less than half* of the FC, or .4324324 (43.24%).

Enough with the math... lets go swimming