How much chlorine per day to maintain?

[Mm_putnam]

I know this is a very subjective question with lots of variables but I'm trying to get an idea from those who've been around the block a few seasons.
Y'all have been a great help in getting our green/cloudy pool to a beautiful/clear body of water. We still have a bit of green algae in the corners that we are doing a so-so job of vacuuming/brushing regularly.
I haven't been extremely regular in testing the water every day but probably every 2nd or 3rd day and pretty much every time I am finding I need to add some bleach. Maybe more than I would expect but that's my quandry - I don't know what to expect.
My last test results were:
This morning
FC - 6.5 (added ~500 ozs of bleach yesterday evening as it was .5)
pH - 7.0

Other readings from a few weeks ago:
CC - none
TA - 70
Calc Hard - 300
CYA 40

So I feel like the levels are in range but I want to know what I should expect for daily FC loss? 50k gallon pool. I know the sun, rain, swimmers, etc. all play a part but can someone give me a typical daily qty to expect? Part of my curiosity is planning (having bleach on hand) and part is to see if I'm having to add more than expected to maintain levels - as in should I shock to get rid of something that's eating my chlorine daily.
Also, I think I understand the the affect of CYA if I go to dichlor instead of bleach but is there an alternative to bleach that y'all'd recommend? I'm all for saving money but I'm willing to pay something for convenience. It's been a lot of big bleach bottles to deal with so I'm interested in some tabs in the skimmer or something that is easier to move around and will distribute evenly. I'm more concerned in using the right stuff by y'all's recommendations but if someone says you could use X as an alternative to bleach and the only real downside is some cost difference - I'd be interested in checking into it.

And I suspect there's a similar thread on this and if so point me to it. I searched a few ways and didn't come across it.

[Watermom]

Does your pool store sell carboys of 10 or 12.5% sodium hypochlorite (liquid chlorine)? That is the same stuff as bleach but at a higher concentration -- bleach is only 6% sodium hypo. That would be a lot more convenient for such a big pool.

[Mm_putnam]

I don't know on the carboys but will inquire. Any ideas on what a reasonable FC loss (per day) is on a 50k gallon pool is? Do most people add a gallon of bleach a day? A half gallon? Less? Trying to get a gauge. Thanks.

[Watermom]

The size of the pool has nothing to do with how fast the chlorine drops. I would say (generally speaking) that you'll lose 3ppm of FC a day. But it depends on weather conditions, swimmer load, the amount of organic debris in the pool, how consistent you are about maintaining adequate chlorine levels, etc.. The amount of bleach most people add isn't gonna do much for you cuz most people don't have a 50K gallon pool! I'm guessing you will need to add 2 or 3 gallons of 6% bleach per day. But that is just a guess.

You might want to bump your CYA up to 50 or so. OR -- maybe even higher. Some people deliberately keep their CYA level high because it allows them to go longer between chlorine additions. The downside to it is that if you don't maintain your chemistry and end up with an algae bloom, your shock level is higher and thus it will require more chlorine to clear the pool up. Janet (Aylad) runs a high CYA pool in Louisiana. She keeps her CYA around 80 or so I believe. I'll ask her to pop in here and offer her comments about this as a possibility for you. Not saying you should do this, but just offering it as another option. But, if you do decide to do this, you MUST maintain adequate chlorine levels at all times. Take a look at the Best Guess Chlorine Chart in my signature above to see the correlation between CYA and chlorine levels.

[aylad]

Hi,

First let me say that you're not getting a true reading of how much chlorine loss you'll have per day, if you still have green algae hanging around anywhere in the pool. As long as there's algae in there anywhere, your chlorine loss per day is going to be higher than it should be, so your first order of business should be to take the pool back up to shock level and hold it there until all that green is gone, and until you can go from sundown one night to sunup the next morning without losing more than 1 ppm of chlorine. Only after you accomplish that are you going to be able to gauge your "normal" chlorine loss. Once that's accomplished, then....

If you will measure your chlorine daily for 5-6 days, you'll get an idea of how much you're losing during the day. Of course, swim load, water additions, etc will be variables, but you can get a rough idea. If you're losing more than 3-4 ppm daily, then I would consider bumping up your CYA to the 50-60 ppm range and see if your chlorine loss doesn't slow down. You'll have to maintain higher base levels of chlorine with the higher CYA, but I think you'll find that you lose less chlorine overall that way.

I don't recommend this for everybody's pool, but just wanted to share my experiences.... my pool is in the northwestern corner of Lousiana. We currently have 102-104 degree temps during the day, down to the high 80s at night. Pool temp right now is 90 degrees. Very little rain, although the humidity stays in the 90%+ range most all the time. My IG pool is in full sun from 8 am until the sun sets over the house, around 6:30 pm. If I run my CYA levels at 40-50, then I lose somewhere between 4-6 ppm of chlorine per day. However, when I run my CYA up to the 80-90 ppm range, my chlorine loss is 2-3 ppm per day. Granted, my chlorine has to stay in the 5-10 ppm range all the time, and when I shock it has to go up to 20 ppm, but with my chlorine loss slowed, I find it much easier to catch the chlorine levels before they get below the 5 ppm so I don't have to shock as often. Besides, it takes no more bleach to shock from 10 ppm to 20 ppm than it does from 5 to 15, which is what you have to do with the lower CYA. So I keep my chlorine around 8-9 ppm, and dose it (roughly 25K gallons--there's a difference in what I was told as a new pool owner and in what the actual volume is, based on the increase in levels when I add chems) with one of the large WalMart jugs of generic bleach every 2-3 days. I end up shocking it about once a month--not because of algae or CC, but because I have a very large swimmer load on a daily basis during the summer (5-8 kids at any one time--right now there are 4 in the pool), and it's more of a preventative measure for me than anything.

So... I don't necessarily recomend that for everybody's pool, but it works very well for me. You could also put a trichlor floater with some tabs in the pool (don't get the ones with copper) for continuous chlorine addition, and just supplement that with bleach, and might even be able to stretch your bleach additions out to 3 days. Just a possibility. IF you decide to try the higher CYA levels, don't just jump from 40 to 90. Take it slow, increase it by about 10-20 ppm increments, and then stop there and measure chlorine loss for a few days before going further. You want to get to the level where your daily chlorine loss is the least, but not high enough that you're having to raise chlorine levels just to keep up without having more added benefit of slowed chlorine loss (does that make sense?) By going in slow increments, you can always "lose" the extra CYA by backwashing or splashout much quicker if you only have to lose 20 ppm rather than 50 ppm, if you happen to pass your most efficient point.

But first, get rid of the green algae, otherwise you're wasting your time and efforts in experimenting with this!

Janet

[Shifty]

Putnam,

Have you tested the CC level since your original post? If your CC is 0, I am surprised you are fighting algae. I would think if you have algae your CC would be in the 1-2 range.