Chlorine loss

[Chaya]

hi,
i have a 21k gallon pool, 60 cya and prone to mustard algae. so based on chart i try to keep my chlorine at about 10ppm.

my pool was beautiful and crystal clear until one day i noticed tremendous chlorine loss - over the day i had to put in 18pmm of chlorine so it didnt drop below my minimum of 10. then i noticed the water was a bit cloudy. didnt see any algae. i figured i had algae and began to shock to 35ppm - the yellow mustard shock levels.

yesterday i tested every two hours and i was loosing about 7-10 ppm in the pool. i then brought the chlorine level back up to 35ppm.

my question is that i was advised previously that at higher PPM, chlorine loss is greater. so i am wondering what WOULD be my chlorine loss per hour if i did NOT have algae? i am curious how much of the loss was just the sunshine and heat at that very high level of chlorine.

also, in any discussion i've posted here, people have told me that my chlorine loss should be 2-4 ppm per day but its more like 6 for me. i'm wondering again if its b/c at higher chlorine levels, you use more chlorine. my pool is in FULL sun the whole day.

Thanks for your help!

 

[Msch99]

Check pool School, but I think you only raise FC to mustard levels after slamming at normal levels.
How long since checked cya? Maybe changed?
High FC loss usually due to algae, high swim load with sunscreen etc or dosing FC higher than cya will protect.

 

[Chaya]

Check pool School, but I think you only raise FC to mustard levels after slamming at normal levels.
How long since checked cya? Maybe changed?
High FC loss usually due to algae, high swim load with sunscreen etc or dosing FC higher than cya will protect.

oh no! so i think i did it wrong. but it shouldnt make a difference, right? if anything my chlorine was too high, it should still kill the algae.

but does anyone know the answer to the normal loss of chlorine rate and 35ppm?

 

[mknauss]

I would first confirm the CYA level. Higher than expected FC loss is typically due to CYA levels being lower than assumed.

Going above SLAM level FC can have an effect on your liner. So be careful doing it for long periods.

 

[Chaya]

i will when i get home but realize my chlorine use was consistently 6pmm and then one day was 18ppm and after that i see that the water WAS cloudy. if i didnt know the correct cya, i should have constant very high usage, not that the usage tripled from one day to the next.

regarding effect on liner, can you tell me what the damage would look like? the last time i replaced my liner (2 yrs ago?) they told me there were pinhole leaks on the bottom of the liner. would high chlorine cause that?

 

[mknauss]

can you tell me what the damage would look like?

Fading is the most prevalent. Especially any blue tinting.

 

[MITBeta]

A "normal" loss of 6ppm per day is pretty high. You've had something going on in your water for a while.