Understanding differences betwen CYA 60 vs CYA 70

[newbie2017]

60​	5​	7-9​	24​
70*​	5​	8-10​	28​

In both cases the minimum FC is 5. Can someone explain the difference in target level that is mentioned? 7-9 vs 8-10

If the pool is losing say 3ppm per day, at both CYA levels we would be targetting 8 or 8.5 right? So what is the actual difference here?

We were at 70, 3 - 4 weeks ago. When I hit 60 , what would we do differently in regards to chlorine additions is my doubt.

Thanks.

 

[Demegrad9]

The minimum FC is always 7.5% of CYA, so for 60 that's 4.5ppm so they just round up to 5ppm. For the 70 row, 7.5% is 5.25ppm so they just round to the closest integer, i.e. 5.

You notice all the recommended range are defined as 10% of the CYA + 2ppm. then just plus or minus 1ppm to define the range. So 60 the range is 8ppm plus or minus 1. And at 70, the range is 9 plus or minus 1.

As you've noticed there's not a lot of difference between 60 and 70 and they have somewhat overlapping ranges.

 

[duraleigh]

The numbers are general guidelines. Don't worry about that small difference.

The test alone has a variance of + - 10 ppm

 

[newbie2017]

Learning something new each day! Thank you.