chlorine use

[Chaya]

Will my pool always use the same amount of chlorine per day (barring changes in temperature, bather load and other external factors)?
So for example, i typically have seen my pool use about 5-6 ppm of chlorine per day. so it starts at about 10 and falls to about 4.5-5ppm by evening. But when i put in MORE chlorine (b/c i didnt want it to fall so low) my chlorine still dipped to the same level. Over the weekend i shocked the pool and brought the pool to about 24 ppm, 1.5 days later, the pool was at 10ppm.

So now i am trying to understand the facts. Will sunlight use up more chlorine over the course of the day if there is more chlorine in the water than if there is a lower level of chlorine in the water?

 

[mknauss]

Yes. The FC loss due to UV is pretty close to a % no matter what FC you have in the water, pending having a reasonable level of CYA in the water.

Your loss of 5-6 ppm FC per day is a bit high for normal. What CYA do you have?

 

[Chaya]

cya of 60
so i'm confused. if the more i put in the more i lose, how do i keep my FC from slipping below the minimum?
i thought i'd just add more chlorine one time to get my morning levels higher so my evening levels would not be below recommended, but it didnt seem to work. i keep dipping below the recommended minimum of 5.

 

[mknauss]

With a CYA of 60, your FC loss per day is high. I would suggest you do a Overnight Chlorine Loss Test one night soon.

 

[Chaya]

i was using that amount and my pool was crystal clear and oclt came back fine.
i will be doing one again tonight.

 

[mknauss]

If crystal clear, no debris on bottom, and you pass OCLT, you should be able to bring the FC up to 9 or 10 ppm in the evening and have at least 5 or 6 ppm left the next evening.

Unless you have multiple swimmers for many hours each day.

 

[Chaya]

during the day my pool is empty but in the evening my kids have tons of friends over. I thought it was the heavy bather load but then one cloudy rainy day the pool was empty and i still used that much.

at some point i must have had some algae b/c i did lose chlorine overnight and i did shock over 2-3 days. So maybe i really did have a problem that was causing the heavy chlorine usage. and maybe i got the algae b/c at the beginning of the season my chlorine kept dipping below recommended levels.

I will definitely keep an eye on it. thank you.

 

[mknauss]

If you had algae and did not complete a SLAM Process to full completion, there is a very good chance you still have algae in your water. Even if you do not see any.

 

[Chaya]

i really think i completed it properly. i brought the level to 24ppm, brushed the pool, tested a few times a day and kept adding more chlroine as it dipped below 24ppm... day, night... kept testing till water was sparkling and clear. i am going to do another OCLT tonight to make sure.

 

[Chaya]

i must have had algae when using so much chlorine past few weeks, because this wk, after completing SLAM at end of last week, my usage is more like 4. thank you for all your help. I didn't pick up on the algae because i was losing like 1ppm overnight and i thought 1 was still ok. but now, after completing SLAM my loss was only .5. the reason i picked up on the algae was because the water, after having been crystal clear, became a little cloudy for a few days, not because of my chlorine use. But now after SLAM its clear again and using less chlorine than at the beginning of the season.