Another shock question

[CarlD]

Alapool:
You've gotten good advice here. You cannot rely on 3ppm as a max--as has been said, 3ppm is the MINIMUM for a CYA level of 30ppm--and running an outdoor pool with less than 30ppm of CYA is an invitation to an algae bloom--because chlorine will disappear due to breakdown and UV rays--sometimes in as little as 15 minutes.

You are probably looking at the EPA's rec that you don't swim in water above 3ppm of chlorine....Yet the same agency recommends that you don't drink water above 4ppm of chlorine--so at 4ppm it's not safe to swim in but it's safe to drink? Bit of a disconnect here, isn't there?

The minimum and maximum safe levels of chlorine depend heavily on the CYA level. Above 10ppm you can get some fading of bathing suits, but that's about it. Swimming pool liners aren't in danger until you reach 15ppm--but that is ONLY for low CYA levels. Again, the CYA affects the chlorine's action.

Your CC should always be zero. However, realistically, using Ben's kit, it frequently has a presence of less than .5--but unless you use the 25ml test (vs the 10ml test) you cannot tell if it's .2 or .4 or .5ppm. This could be due to pollen, suntan lotion--any slight contaminant--and it's hard sometimes to get that last bit of CC gone--I generally run my FC between 4 and 8ppm and that darn "<.5" shows up. But if it's clearly .5 or greater, you need to shock to get it down.

[Lenny]

However, realistically, using Ben's kit, it frequently has a presence of less than .5--but unless you use the 25ml test (vs the 10ml test) you cannot tell if it's .2 or .4 or .5ppm.

Carl,

Are you just talking about using the same test kit and just changing the proportions? I don't think I saw that listed as an option in the instructions.

Lenny

[CarlD]

If you look at the DPD-FAS test, there are two ways to use it:
1) with 10ml of pool water. Then each drop of the re-agent represents .5 ppm
2) with 25ml of pool water. Then each drop of the re-agent represents .2ppm, allowing greater precision.