Trying to weigh cost of bleach vs. SWG

[shooter57]

I'm doing the calculations to try to make an educated decision on whether or not to buy a SWG.

I've read here that losing 1/2 of the FC each day is a reasonable expectation. My FC target is 6, so that would be a loss of 3 ppm of bleach each day. The Pool Calculator tells me that for a 27Kgal pool that would be 170 oz of 6% bleach per day.

We swim from May to October, and obviously the target levels for all chems apply during that time. How do I calculate the chemical usage during the off season? (We don't actually close the pool, but I'd imagine with different atmospheric conditions and pool use that the demand would change or do I maintain the same target numbers all year?)

Using the 3 ppm FC loss value over 12 months, it comes out to 478 gallons/year. Buying bleach at Costco (three 182 oz jugs for $6.99) I'm looking at $784/year in Clorox. Wow.

At that rate, the return on investment for a SWG seems like a no brainer. Should I be figuring the same bleach usage amount all year long?

If I went with the SWG, what should I estimate for the cost of electricity for the SWG? Salt?

Thanks in advance for any help. I apologize if this was too many questions or too much info, I wanted to try and be thorough.

 

[PaulR]

Because the bulk of the FC loss is due to sunlight, you should see distinctly less chlorine use in the winter.

Are you losing 3ppm per day now? That feels a little high.

A cover will help reduce FC loss. That works for bleach or SWG, actually. Even if you can't be bothered during the season, using one in the winter will help.

Remember that an SWG is not a one-time cost, periodically you need to replace the cell.
--paulr

 

[polyvue]

A cover will help reduce FC loss. That works for bleach or SWG, actually. Even if you can't be bothered during the season, using one in the winter will help.

Yup. But I find that a cover is more helpful in late spring/summer/early fall because the chlorine takes more of a beating from the UV (the sun is higher in the sky and longer exposure.) In the winter, I don't bother to use a cover and my chlorine depletion is minimal. I think this is partly due to the water temperature (48°-60° F.)

If I went with the SWG, what should I estimate for the cost of electricity for the SWG? Salt?

Keep meaning to do a calculation on this, but am just this month formulating a cost for existing pumps and don't have specifications for my Goldline Aqua Logic SWG cell (it's the super-duper 40K gallon model). Salt is cheap by the bag, but if you get a lot of spash-out as I do you'll find yourself running to the pool store every few months to stock up. The electricity (I'm guessing) will be a small fraction of what a pump costs to operate. The main cost, as Paul noted, is the initial expenditure and the (eventual) cost of replacement. Someone else may have done this work already, but if not, I'll post an estimated annual cost... soon.

 

[shooter57]

Are you losing 3ppm per day now? That feels a little high.

Seems to be about 2 ppm currently. The pool cover is on throughout the season.

If the loss were to remain constant thru the year that puts me at only $500 a year for bleach. Based on replies, the FC loss should decrease during winter and may increase during the peak of the summer. Still seems like a lot of money for bleach, I can see why the pucks are so popular. It only cost me about $150 to drain and refill the pool, and I used to use about $100 worth of chlorine tabs a year. Based purely on those financials, it seems to make more sense to go with the floaters and swap the water out more often. Where is the fault with this logic?

 

[beaumatt]

WOW, only $100 bucks a year for Chlorine Tabs? My 20,000 gal used about 2 1/2 pails/year (May-Sept) and at a minimum of $105 a pail, I spend at least twice as mine in mine. I have preliminarily checked out SWG, but they seem incredibly expensive to me when you consider all the costs involved. To me it makes more sense to pour in a little bleach every day.

 

[duraleigh]

There have been many cost comparisons done on this forum in the past. Bleach usually comes out the cheapest but not by too much.

Cost is not the reason for using bleach, however. It is that bleach adds no other chemistry to your pool whereas most other forms of chlorination do. A well managed pool can stay in balance using more than one source of chlorination but bleach (liquid chlorine) is the simplest and has virtually no unwanted side effects.

An SWG will be the least cost effective.....but you have to consider the convenience and what it's worth to you.

My bleach costs are somewhere around 175.00 annually for a 43k pool. I haven't looked carefully at your math but $500 annually has a miscalculation in there somewhere.

 

[frustratedpoolmom]

Based purely on those financials, it seems to make more sense to go with the floaters and swap the water out more often. Where is the fault with this logic?

It is an option, certainly. The key about TFP is knowledge. Proper testing. So as long as you know what side effects tablets have on the chemistry and take the proper steps, you can certainly go that route. But in many areas draining isn't an option (drought conditions/water rationing). Are you factoring in the PH/TA adjustments when you calculate $100?

What kind of cover do you have? I lose virtually zero FC with my dk blue solar cover on the pool. Do you have a lot of organics dropping in the pool? 2ppm with the cover on seems excessive to me.

 

[DBfan187]

In most cases a SWG is going to break even or you end up spending more money. Once you factor in the initial cost, frequent buyings of salt, acid, stabilizer, and any other chemicals you may need, electrical rates, and then the cost of a replacement cell down the road.

 

[mas985]

Shooter57,

What is your CYA level?

50% loss per day is consistent with a fairly low CYA level. So if your operating around 25 ppm of CYA, it makes sense. But then you could drop your FC level so you wouldn't lose so much FC.

A FC level of 6 ppm is reflective of a CYA of 50 ppm and if your CYA is that high, then I would expect a FC loss of about 25% per day which would mean something else is eating the chlorine.

 

[chem geek]

2 ppm FC per day in 27,000 gallons for one month would require 3360 fluid ounces of 6% bleach which is ($6.99/3*182)*3360 = $43 per month during the peak season. During the off-season with cooler pool temps (below 70F and especially below 60F) the chlorine usage drops dramatically to as low as 1 ppm FC per week. Realistically, you probably don't have more than the equivalent of an 8-month peak season for the year so that would be around $344 for the year and that's probably on the high side.

As described in this post, Trichlor is more expensive than bleach when accounting for the pH Up or equivalent chemical you need to add to maintain the pH and TA. However, if you used only Trichlor, your CYA would get much higher which in the short-run could lead to lower chlorine usage with more protection from sunlight, but then at some point algae would start to grow and the chlorine demand would go up.

As was noted, 2 ppm FC per day is a bit high when using a pool cover. That cover must not be opaque to UV. My cover is (mostly) opaque and the chlorine usage is a little less than 1 ppm FC per day in a 16,000 gallon pool with water temps at 86-90F. My monthly chemical costs are around $17 per month for a 7-month swim season (off-season chlorine costs are negligible at perhaps $10-15 for the entire 5 months).

 

[shooter57]

Shooter57, What is your CYA level?

mas - my CYA is 40. Funny, after having a CYA level of about 200 (off the scale for my test kit) I was stoked to finally be reading 40 after draining and refilling the pool. That number is a little below mid range based on my goal numbers, but within range based on the Pool Calculator numbers. After fighting high CYA for a long time I'm a little gun shy about jacking it up.

50% loss per day is consistent with a fairly low CYA level. So if your operating around 25 ppm of CYA, it makes sense. But then you could drop your FC level so you wouldn't lose so much FC.
A FC level of 6 ppm is reflective of a CYA of 50 ppm and if your CYA is that high, then I would expect a FC loss of about 25% per day which would mean something else is eating the chlorine.

I know with my previous CYA levels I could not keep chlorine in the pool. Does having too low of a CYA level have the same effect?

 

[frustratedpoolmom]

If your CYA is too low the sunlight consumes more of the FC... sometimes its a regional thing and we recommend a higher CYA level of 50-60 etc. But if your solar cover is on, that should block some of those UV rays too... unless your cover is perhaps clear or not opaque? My chlorine usage is similar to Richards and I would say in the heat of the summer my costs are about $12 for my AG pool (light bather load, few trees to drop leaves in) but 2-3 ppm per day with the cover on and no swimmers is a lot.

 

[mas985]

With the cover and a CYA of 40, I wouldn't expect the FC loss to be that high. So it sounds as though something else is using it up. What is your CC level?

 

[Pontiac]

There are some characteristics about Morgan Hill that need to be considered.
It gets hot there. Its an agricultural area with large areas of open ground. And it's windy, especially in the late afternoon.

Add that all together, and a 2ppm FC loss for that area is not all that uncommon.

 

[shooter57]

With the cover and a CYA of 40, I wouldn't expect the FC loss to be that high. So it sounds as though something else is using it up. What is your CC level?

CC is 0.

Current numbers:

FC - 3 to 6 (depending on time of day)
TC - same
CC - 0
pH - 7.4 (aerating to bring this up)
TA - 120 (adding muriatic acid to bring this down, hence the low pH)
CH - 300
CYA - 40

Yes, my cover is clear not opaque. Prior to finding this forum my only concern in a cover was evaporation and heating. We found the clear cover to be significantly better at heating the pool. The cover is slightly smaller than the pool this year, I ordered from memory and got the wrong size. Oh well, it's only off by a foot or so.

Pool was drained about 90% and refilled in early summer, CYA was 40 then and hasn't changed. CH was down and TA was up, pH was right where it should have been. We brought the CH up and are now working on the TA/pH balance.

BTW, in case I hadn't made it clear before I truly appreciate all the help, suggestions and feedback. I want to understand the chemistry involved. Any perceived challenges are just me trying to make sense of things.

 

[mas985]

There are some characteristics about Morgan Hill that need to be considered.
It gets hot there. Its an agricultural area with large areas of open ground. And it's windy, especially in the late afternoon.

Add that all together, and a 2ppm FC loss for that area is not all that uncommon.

Pleasanton is not that much different than Morgan Hill. We have had 100 degree weather this week. With a CYA of 40 ppm and a FC of 4 ppm, I still only lose 1 ppm per day. That is 25% compared to 50% and I am not using a cover. Plus my pool is in the sun all day. 50% still seems a bit high to me. Maybe there is an animal peeing in the pool at night. :lol:

shooter57, Did you do the CYA test yourself or did a pool store do it? Pool stores are notorious for poor CYA measurements so I just wanted to check. Also, if you did it yourself, did you make sure that the dot was completely obscured? Also, do you lose any chlorine overnight?

 

[shooter57]

shooter57, Did you do the CYA test yourself or did a pool store do it? Pool stores are notorious for poor CYA measurements so I just wanted to check. Also, if you did it yourself, did you make sure that the dot was completely obscured? Also, do you lose any chlorine overnight?

Mark - I did the CYA test myself, I learned to distrust pools stores shortly after I started using them. Yes, the dot was completely obscured. Great question, though, always good to be sure of the facts.

 

[mas985]

Ok, so does the chlorine hold overnight? If so, then I am at a loss to explain it but it will not be any different with a SWG. You might want to try a higher CYA level first to see if that helps, if so, it is the sun causing the problem, if not something else is using it up.

 

[H2O_Keeper]

I have weighed it out both ways SWG vs chlorine and for me it made more sense to hang on to the $1K and use bleach. In my case the swim season is from May to Sept. For 5 months of bleach vs the cost of salt, its additions, electricity, and the reports of a good life of 3 years for the cell it just didn't make sense. If I lived somewhere with a lot longer swim season then yes I would consider a SWG.

The curve for those five months vary (per ChemGeek). The beginning and end of the season I use mabye .5FC a day and midseason I use 1-2FC.....Per the others it maybe your FC/CYA ratios or something else consumng FC.

 

[New2Me]

Hi Shooter,
Here is a link to some calcs I made last year, keep in mind that I got the least expensive Chlorine Generator I could find, bleach here is fairly in-expensive, as is the abundant coal generated electricity.
http://www.troublefreepool.com/actual-swg-vs-bleach-cost-eye-popping-t9338.html

If you are using bleach now, keep track of your daily usage, and you can convert it to how much actual chlorine you need daily, and can size a generator to match that demand to your pump run time by taking the cells rated daily generation/24 to get an hourly chlorine production, and matching that up to your actual chlorine demand / by your pump run time(in hours.)

I just finished my first full-year usage of the CG, but I'm still keeping bleach and tablets on hand. Starting with a fresh fill, you need to add salt, CYA and Chlorine, before you can use a CG. A CG is for MAINTAINING a FC level only, it is not for establishing one.

I don't know what your acid usage is, mine was zero with tablets and bleach(thanks to acid rain?,) but I now use ~1 quart a week, and I have 50 ppm Borates ( and it has been a crappy summer with ALOT of rain.) With out the borates, I think that my acid usage would be higher.

And also remember that you should not use dry acid with a CG.

In the middle of summer last year I was using 1/2 gallon of 6% every day, for a 24,000 gallon pool with a CYA of 80-90. At $1.50/gallon($1.15 small jug) x (~150 day season)=$112.5 for a seasons worth of bleach. A gallon of MA is ~$3 on sale here, x 21 weeks =$63 for a seasons worth of acid. Salt and borates are a one-time expense(~$150, including the MA.) The largest CG will use ~ 500 watts when its running, more then a computer, but less then a hair-dryer. How long your pump will need to run to generate your required amount of chlorine will be much more important(watt-wise.)

Even in my case, bleach is hands down less expensive. I'm going to continue to pay the cost for convenience, though. Now, when this CG craps out (and it will sooner then one that was more expensive, I'm sure,) it will depend on replacement cell cost as to whether I go back to BBB.
Best Wishes!