How much chlorine consumption is "normal"

[mopoco]

I've gotten my pool balanced after firing my pool guy. I have a question about how much chlorine usage/loss is normal for a pool similar to mine. When I read the threads, it seems like mine is using considerably higher amounts. After dumping the pool guy, I drained the pool to get the CYA lower, down to ~55ppm. Chlorine usage was about 96 - 110 oz per day (6% Chlorox), for 11000 gal, it would be about 4.5ppm/day. I added CYA, to bring it up to about 60, and now my daily usage is about 84-96 oz per day (3.5-4.0 ppm/day). Overnight chlorine loss is consistently about 1ppm.

My numbers are:
FC - 5
CC - 0
pH - 7.7
TA - 80
CH - 290
CYA - 60
Pool temperature ranges from 85-94, depending on ambient conditions and whether or not I'm aerating overnight.

So, the questions are:
1. Is this amount of chlorine usage above normal for hot, sunny Arizona?
2. Should I increase the CYA to reduce daytime loss of chlorine due to UV exposure?

Thanks for all the great info. My pool is finally consistently clear and inviting!

 

[Bama Rambler]

If your overnight chlorine loss is consistantly 1ppm you may have a slight problem. I know we say 1ppm or less but if it's consistant there may be something going on. It could just be your testing times.

In Az you might raise your CYA up to 70 and see if that helps. But be sure before you do that, that there's absolutely no organics helping you out with your chlorine consumption.

 

[woodyp]

4-5 ppm might be "your" normal if it has full sun all day. Mine runs like that. I take the target FC to 2 points higher to keep my minimum for the cya level intact.

 

[tim_pool_newbie]

I recently posed a very similar question. See my original post for that discussion.

I was also thinking that perhaps if I increased the CYA level a bit, it would add a bit more stability to my chlorine and therefore I'd see less chlorine loss each day. In theory that makes sense, but in reality it was pointed out to me that by raising my CYA level, I run the risk of getting into the danger zone of NO protection at some point, and then finding myself doing a partial drain/refill.

For me, in PA where my pool gets lots of direct sunlight all day, I just accepted the fact that my pool requires about 3 quarts (or more) of chlorine per day in order to stay within the proper FC levels for my pool.

Next year I'm seriously considering automating this process with a Liquidator, or perhaps even a SWG if I can afford it.

 

[mopoco]

If your overnight chlorine loss is consistantly 1ppm you may have a slight problem. I know we say 1ppm or less but if it's consistant there may be something going on. It could just be your testing times.

In Az you might raise your CYA up to 70 and see if that helps. But be sure before you do that, that there's absolutely no organics helping you out with your chlorine consumption.

So to be sure I have absolutely no organics, do you recommend shocking? I did shock it about a month ago because the pool guy never kept the FC high enough to compensate for the high CYA. I thought I had done a good shock, but near the end I ran out of titrants, and couldn't verify my levels. After getting the titrants, I found that the FC had dropped down to about 12 (if I remember right), but the overnight FC loss had dropped to 1ppm, so I figured it was good.

 

[woodyp]

Why shock??? CC=0 and if the water is clear with no algae. No problems.

 

[Sportsman]

You say 1ppm overnight loss. I'm sure your sun is beating down early in the morning. Are you truly testing before the sun hits the pool? Might be worth making sure to test after dusk/before dawn one day (if that's not what you're already doing) before shocking.

Another consideration is I thought I was having an overnight loss earlier this week but ran my pump 30 minutes and tested again an hour after sun-up and there was no overnight loss. I recently read somewhere on here the recomendation to run the pump before tests and have not incorporated that into my routine.

 

[Guest]

I would think your numbers are pretty accurate based on your daily temperatures in Chandler. When your that hot and I suspect your pool temps are in the 90's?? Sounds like your ahead of the curve. Keep doing what your doing!

 

[chem geek]

Hotter pool water will consume chlorine even when there isn't any algae or bather load. In my own pool at 86-90ºF water temperature, the pool would consume around 0.7 ppm FC per day if there were no bather load and no sunlight (it has a mostly opaque cover). With 1-2 hour use per day and longer on weekends, I'm at around 1 ppm FC per day. It's low due to the mostly opaque electric safety cover.

Even so, 1 ppm FC loss overnight seems high, but perhaps if the water is hotter than 90ºF then that's possible. However, even in a hot 104ºF spa, chlorine loss is usually around 25% of the FC level or around 1 ppm over 24 hours if the FC is at 4 ppm to start with. At least some of this chlorine consumption is due to the slow oxidation of CYA -- at 5 ppm per month CYA loss that uses up 12.5 ppm FC that's around 0.4 ppm FC per day.

You might check to make sure there isn't anything in your filter, under any removable steps, behind light niches, in skimmers and pump baskets, etc. that might be consuming chlorine. You could always shock to be sure to kill off any nascent growth and of course should brush the pool to disrupt any biofilm that may have formed if the chlorine ever got too low.

 

[mopoco]

You might check to make sure there isn't anything in your filter, under any removable steps, behind light niches, in skimmers and pump baskets, etc. that might be consuming chlorine. You could always shock to be sure to kill off any nascent growth and of course should brush the pool to disrupt any biofilm that may have formed if the chlorine ever got too low.

Good thought. I do have a light that could have algae behind it, and of course, I'll double check the pump baskets, etc. To check the filter, do you think I need to do a teardown and thorough cleaning of the DE grids, or is a backwash sufficient?

Thanks!

 

[chem geek]

Just check the clarity of the water from a backwash. That should be sufficient unless you believe you could have very uneven water flow in your filter leading to "dead spots".