What to do first? CYA > 200 ppm

[PoolLizard]

Hello,

21,500 gal, IG pool. Just got a new K-2006 test kit and here are the test results:

FC = 4.4
CC = 0.2
pH = 7.4
TA = 150
CH = 560
CYA = 200+ (I'm guessing here. It's way beyond the scale)

Fill water CH = 60ppm.


From what I've read, the most recommended way of lowering CH, and CYA, is to drain and refill. But, somewhere else on this forum I read a post by PoolDoc of another way. I can't find that thread now. So, what's the best/cheapest path for me to take?

[PoolDoc]

1. Assuming your pool is algae free, raise your chlorine level to above 10, and keep it there, till you have more information and another plan. When CYA > 100 ppm, swimming with chlorine > 20 ppm is no problem. Use the 10ml sample to test chlorine, so you don't use up your R0871 drops.

2. Read the Best Guess page, linked in my blue signature block.

3. Tell me if you have any sort of heater or salt water chlorination system. Tell me if you are currently having any scale appear.

4. Tell me what kind of pool you have (vinyl, FG or concrete) and whether the ground is dry in your location. (S Calif, so I assume it is, but please confirm).

5. Do NOT use any algaecides or other such products.

6. Mix 1 cup of pool water with 1 cup of tap water. Test CYA levels in the mix. Multiply result x2 for actual pool CYA level.

7. Tell me what you've been using to chlorinate.

8. If you have NOT been using cal hypo, but have some idea where the calcium came from, please explain.

9. Do NOT worry about CC levels, even if they go up a bit.

10. Tell me what sort of filter you have.


Good luck!

[PoolDoc]

Hm-mh. I just processed your registration and upgraded your membership -- you included your address, and Google Maps has a high res of your pool . . . SO I can see ground water won't be a problem. Unless you've just had a flash flood, you can drain safely.

Unless water is very expensive, or there are no-drain rules in place It would certainly be easier to drain, than to do lime-softening.

But, lime softening would probably be cheaper . . . IF you have a way to vacuum to waste. What will happen is you'll deposit lime dust all over the bottom of your pool, and then have to vacuum it out, dumping it on the ground. Afterwards, you'll have VERY high alkalinity, and will have to lower it. You'll probably replace a foot of water.

However, this will NOT lower your CYA more than what would be removed with 1 foot of water, so we need a better idea on your real CYA level. The only practical way to lower CYA is to let it be biodegraded, which means DELIBERATELY letting your pool get slimy for several weeks. Even then, it's a crap shoot -- with no guarantees. The right bacteria may not show up, OR you may find that the CYA degrades to ammonia (HUGE mess) rather than nitrogen gas. So, it's a risk, not worth taking unless the water situation is dire, and your CYA is truly too high to handle. DO read the Best Guess page.

[PoolLizard]

Thank you PoolDoc/Ben - I will be working on your list today, I'll get back with a complete report as soon as I can.

I'd like to go ahead a drain about a foot of water, and refill, BEFORE I put in a lot of new chlorine. And then see where the readings are. I'd like to see how much replacing one foot of water will help. Water here is very expensive, but I've come to the conclusion that I have to "bite the bullet" anyway.

Suggestions?

Thanks!

PoolLizard

[PoolDoc]

Before you drain, you need to decide whether you want to do lime-softening to remove calcium. If you do, you'll end up draining and replacing a foot of water, as part of that process. What I'd recommend is that you follow this sequence:

1. Raise your chlorine level and keep it there

2. Retest with the K2006, to verify the high calcium, and to do the dilution test on the CYA

3. Report how the calcium arrived in your pool. This is very important -- it will do no good to remove some calcium, if it's just going be added again, somehow or other.

4. Make SURE you understand the Best Guess page, and then let me explain what it requires to run the HiC2 method (high CYA / high chlorine). If you do NOT want to do this, and your CYA is actually > 200 ppm, you'll have to drain 75% or more at one time in order to use more standard chlorine levels.

5. THEN look at all this info with me, and make some decisions about what to do. BUT, it's important to get the chlorine up NOW, so you aren't forced into dealing with an expensive, time-consuming, and ultimately wasteful algae problem.

[PoolLizard]

I'm going to go ahead and answer as many of your questions as I can right now, and complete the rest later. See my responses inside [] brackets.


1. Assuming your pool is algae free, raise your chlorine level to above 10, and keep it there, till you have more information and another plan. When CYA > 100 ppm, swimming with chlorine > 20 ppm is no problem. Use the 10ml sample to test chlorine, so you don't use up your R0871 drops.
[Upon your approval, I'm going to replace about a foot of water, then do a complete water test to see where the numbers are. Then raise the chlorine level.]


2. Read the Best Guess page, linked in my blue signature block.
[Done, but I may have to reread it a few times to completely understand.]


3. Tell me if you have any sort of heater or salt water chlorination system. Tell me if you are currently having any scale appear.
[I do have a gas heater, but it is not used, it is bypassed. No salt system.]


4. Tell me what kind of pool you have (vinyl, FG or concrete) and whether the ground is dry in your location. (S Calif, so I assume it is, but please confirm).
[I believe it is a concrete pool. Yes, the ground around the pool is dry. This is in the Mojave Desert.]


5. Do NOT use any algaecides or other such products.
[Just before I registered in the forum, I had put 3 ounces of HTH Super Algae Control into the pool. Okay, I won't use any more. ]


6. Mix 1 cup of pool water with 1 cup of tap water. Test CYA levels in the mix. Multiply result x2 for actual pool CYA level.
[Okay, will do.]


7. Tell me what you've been using to chlorinate.
[I *had* been using Trichlor tabs in two floaters, and Calcium Hypochlorite granuals, until I started reading this forum. I have pulled the floaters out, and switched to 10% bleach liquid chlorine. I basically have ignored this pool for the last 9 years. I had a job that required me to travel 200 miles round trip each workday. All I had time to do was eat, sleep and work. Now, I am retired and so I have more time to attend to the pool. So, just this summer I have gotten serious about getting the pool in ship shape.]


8. If you have NOT been using cal hypo, but have some idea where the calcium came from, please explain.
[See #7 answer.]


9. Do NOT worry about CC levels, even if they go up a bit.
[Okay]


10. Tell me what sort of filter you have.
[I have a PAC-FAB FNS 60 DE filter with just a simple push-pull up and down backwash valve.]

[PoolLizard]

Before you drain, you need to decide whether you want to do lime-softening to remove calcium. If you do, you'll end up draining and replacing a foot of water, as part of that process. What I'd recommend is that you follow this sequence:

1. Raise your chlorine level and keep it there

2. Retest with the K2006, to verify the high calcium, and to do the dilution test on the CYA

3. Report how the calcium arrived in your pool. This is very important -- it will do no good to remove some calcium, if it's just going be added again, somehow or other.

4. Make SURE you understand the Best Guess page, and then let me explain what it requires to run the HiC2 method (high CYA / high chlorine). If you do NOT want to do this, and your CYA is actually > 200 ppm, you'll have to drain 75% or more at one time in order to use more standard chlorine levels.

5. THEN look at all this info with me, and make some decisions about what to do. BUT, it's important to get the chlorine up NOW, so you aren't forced into dealing with an expensive, time-consuming, and ultimately wasteful algae problem.


Okay, I'll go ahead and raise the chlorine level up today. And I'll check the CYA using the 10ml sample method.

I'll let you know when that's all done.

Thanks!

[PoolDoc]

Good.

The fact that you have a DE filter with a slide valve means vacuuming to waste would be difficult -- you'd have to add some valves. That makes it impractical to use the whole pool lime-softening technique, at least for now. But there may be some intermediate steps you can follow.

One point I should emphasize is that the so-called BBB method I originated (I came up with the method, not the name) is not literally bleach / borax / baking soda: rather those products are more symbolic of the approach of using the easiest, cheapest and best way to care for your pool. And one of the fundamental points of the BBB method is that you have a POOL, not a 'set of test numbers'. So, we don't worry too much about numbers, when they aren't causing a problem.

Unlike pool stores, who want to sell chemicals, we try to avoid fixing what's not broken!

In your case, if you have no tile-line scale . . . you are NOT having a calcium problem, even if your level IS 560 ppm. So, let's get more accurate info on your numbers, raise the chlorine, and then re-assess.

[PoolLizard]

Good.

The fact that you have a DE filter with a slide valve means vacuuming to waste would be difficult -- you'd have to add some valves. That makes it impractical to use the whole pool lime-softening technique, at least for now. But there may be some intermediate steps you can follow.

One point I should emphasize is that the so-called BBB method I originated (I came up with the method, not the name) is not literally bleach / borax / baking soda: rather those products are more symbolic of the approach of using the easiest, cheapest and best way to care for your pool. And one of the fundamental points of the BBB method is that you have a POOL, not a 'set of test numbers'. So, we don't worry too much about numbers, when they aren't causing a problem.

Unlike pool stores, who want to sell chemicals, we try to avoid fixing what's not broken!

In your case, if you have no tile-line scale . . . you are NOT having a calcium problem, even if your level IS 560 ppm. So, let's get more accurate info on your numbers, raise the chlorine, and then re-assess.


Okay, I just got done dumping 442 ounces of 6% bleach into the water. How long do I wait before I do a chlorine test? The pump is running at 3110 rpm right now.

Oh, I do have a scale ring. Plus, I think I have scale buildup on the bottom too. I'll see if I can get some pictures of the bottom.

[PoolDoc]

2 hours should be plenty, to wait. It sort of depends how your pool's circulation system is set up, but regardless, 2 hours should be enough.

Pictures of both tile & bottom, if you can, please. Post them, or links to them, using Webshots, Flickr, Google Drive, etc, or email them to poolforum@gmail.com. To take the pool into a scale-removing state will be a bit tricky, but I've thought of a way that may work.

Also, take pictures of your equipment. PacFab changed their name to Pentair a long time ago; how much like your filter is this one: http://www.pentairpool.com/pool-pro/products/filters-de-fns-plus-filters-61.htm ?

[PoolLizard]

Here are some pictures:

Complete pad:

http://i1093.photobucket.com/albums/i426/_JerryVB_/MyPool/P1000708.jpg

Filter:

http://i1093.photobucket.com/albums/i426/_JerryVB_/MyPool/P1000710.jpg
http://i1093.photobucket.com/albums/i426/_JerryVB_/MyPool/P1000711.jpg

Pump:

http://i1093.photobucket.com/albums/i426/_JerryVB_/MyPool/P1000713.jpg

Scale:

http://i1093.photobucket.com/albums/i426/_JerryVB_/MyPool/IMGP0254.jpg
http://i1093.photobucket.com/albums/i426/_JerryVB_/MyPool/IMGP0253.jpg
http://i1093.photobucket.com/albums/i426/_JerryVB_/MyPool/IMGP0252.jpg
http://i1093.photobucket.com/albums/i426/_JerryVB_/MyPool/IMGP0251.jpg

Hope this helps.

Will go test water now.

[PoolLizard]

At 13:45 pm my time, the FC level is now 5.5.

Adding more bleach. And testing CYA.

[PoolLizard]

At 14:30 the CYA = 240. I mixed 7ml of pool water with 14 ml of tap water. Took 7ml of that for the test. Reading was 80. 80 x 3 = 240.

Also, added another 128 oz of 10% bleach.

[PoolLizard]

At 16:15 pm, the FC is now 10. Yeah!

What's next?

[PoolDoc]

OK, time for a decision. You have two options.

1. You can run a HiC2 pool (chlorine above 10 ppm, dosing 1x per week, etc) AND you can work on lowering your calcium by adding soda ash slowly upstream of your filter. Each time you do this, you will collect some calcium carbonate on the filter, but some more will cloud the pool. You'll have to turn the pump off for 12 - 24 hours to let the calcium settle, then vacuum it up and clean your filter. I'm not sure how much calcium you'll be able to remove on each pass.

OR

2. You can drain most of your pool and refill. To reach CYA = 80 ppm, you'll need to drain 2/3 of the pool. This will also lower your calcium hardness to around 230 ppm. This would be easiest; but whether it's best depends on your preference and how much water costs there. Obviously, the first option will be cheapest, even when you allow for spending $100 on soda ash, acid, and extra DE.

[PoolLizard]

OK, time for a decision. You have two options.

1. You can run a HiC2 pool (chlorine above 10 ppm, dosing 1x per week, etc) AND you can work on lowering your calcium by adding soda ash slowly upstream of your filter. Each time you do this, you will collect some calcium carbonate on the filter, but some more will cloud the pool. You'll have to turn the pump off for 12 - 24 hours to let the calcium settle, then vacuum it up and clean your filter. I'm not sure how much calcium you'll be able to remove on each pass.

OR

2. You can drain most of your pool and refill. To reach CYA = 80 ppm, you'll need to drain 2/3 of the pool. This will also lower your calcium hardness to around 230 ppm. This would be easiest; but whether it's best depends on your preference and how much water costs there. Obviously, the first option will be cheapest, even when you allow for spending $100 on soda ash, acid, and extra DE.


I did some calculations on water cost based on my last water bill, and it seems that it wouldn't be as costly as I had feared. I'm going to verify that with the Water Co tomorrow. If I'm right, then I'll be doing a drain and refill sometime this week. If my estimates are correct, it would cost around $120 to completely drain and refill. Does that sound reasonable, or am I way off?

On my bill, 1 unit = 100 Cubic Feet of water = 748 gallons. According to my last bill, 1 CCF (748 gal) = $4.55. 20,000 gals divided by 748 = 26.74. 26.74 X $4.55 = $121.66.

I hope I'm right.

[PoolDoc]

If you can drain and refill for ~$120, that's definitely the way I'd go. Because you have some scale, I'd recommend doing a 100% drain, and NOT adding any calcium or alkalinity (baking soda) for awhile. If the pH is too low, use borax to raise it. That way, you have the option of running a low calcium low pH pool long enough to soften and then remove the scale.

I would call the water company though -- they can have some funky ways of calculating bills. And, get the name and position of the person who helped you. That way, if you get a bill next month for $400 because of some bill-calculating funkiness, you can credibly do the whole, "But sir, I was told by your staff . . .", etc. routine.

[PoolLizard]

If you can drain and refill for ~$120, that's definitely the way I'd go. Because you have some scale, I'd recommend doing a 100% drain, and NOT adding any calcium or alkalinity (baking soda) for awhile. If the pH is too low, use borax to raise it. That way, you have the option of running a low calcium low pH pool long enough to soften and then remove the scale.

I would call the water company though -- they can have some funky ways of calculating bills. And, get the name and position of the person who helped you. That way, if you get a bill next month for $400 because of some bill-calculating funkiness, you can credibly do the whole, "But sir, I was told by your staff . . .", etc. routine.


Thanks. Yeah, I'm definately going to verify my estimate with the Water Co before I drain. I know their address, I'm going to go right into their office and have a chat with them.

[PoolLizard]

It looks so good, I hate to have to drain it!

905

[PoolDoc]

Well, it's still your call. I assume that algae is not the problem in the desert that it is here, where every tiny breeze carries spores.

Contrary to pool industry literature, there's nothing wrong with running a HiC2 pool, if you understand what you're doing.

[PoolLizard]

Well, it's still your call. I assume that algae is not the problem in the desert that it is here, where every tiny breeze carries spores.

Contrary to pool industry literature, there's nothing wrong with running a HiC2 pool, if you understand what you're doing.


Algae has been a slight problem. I think only because I didn't know what I was doing, not knowing about CYA, until just recently. If my water cost estimate is close, I'll go ahead with the drain/refill because I want the chemistry to be right, and to try to get rid of the scale.

[CarlD]

Oh, just so you know, the cheapest way to get Soda Ash is to go to your grocery store and buy Arm and Hammer WASHING Soda, in the yellow box (not baking soda). Washing Soda is IDENTICAL to the pool store pH raisers but costs far less--around $.80/lb here in NJ. pH Raisers like pH Up! are nothing but Sodium Carbonate...Washing Soda.

That may well change your cost basis for the soda ash method.

[PoolLizard]

Oh, just so you know, the cheapest way to get Soda Ash is to go to your grocery store and buy Arm and Hammer WASHING Soda, in the yellow box (not baking soda). Washing Soda is IDENTICAL to the pool store pH raisers but costs far less--around $.80/lb here in NJ. pH Raisers like pH Up! are nothing but Sodium Carbonate...Washing Soda.

That may well change your cost basis for the soda ash method.


Thanks, Carl, I'll remember that.

[PoolLizard]

If/when I do a complete refill, should I follow PoolDoc's instructions here: http://tinyurl.com/lyu7bnr ?

Question though: I have not been able to find any commercial bleach in the local stores with a chlorine % on the bottle. And, most of them don't come in gallon jugs anymore! So, I've been buying 96 oz jugs at a local grocery store. Label name is "VALU TIME Bleach". I tried to find an MSDS for this product online and was unseccessful.

I did determine that one bottle of that bleach raises my FC level by one point.

So, what I'm getting at is, what and how much chemicals do I need to have on hand for the refill? I want to be prepared.

[PoolLizard]

Well, water is flowing. Started about 15 mins ago. I talked to a Water Co rep this morning. She said it would cost between $80 to $100 to refill. I think she's a little on the low side, but at least her estimate wasn't horribly high either.

[PoolDoc]

Good deal.

[PoolLizard]

Had some black algae spots on the bottom of the pool. Removed them with a wire brush. Refill is now in progress.

[PoolDoc]

Sounds good.

[PoolLizard]

Pool is about 1/3rd to 1/2 full. I poured in one 96 oz jug of (?)% store bought bleach. I know, there's no CYA in the water yet, but with these high outside temps (98 at the moment, and going up), I just wanted to get at least some chlorine in the water. I swished the water all around with my pool brush.

[PoolDoc]

Best time to add chlorine -- ESPECIALLY on a pool with low CYA -- is in the late evening.

[PoolLizard]

Best time to add chlorine -- ESPECIALLY on a pool with low CYA -- is in the late evening.


Understand, point well taken.

[PoolLizard]

Well, refill almost complete. Water level has about 8 inches to go.

I have my Bleach, Borax, and Baking Soda ready. As soon as the water gets up to skimmer level I'll get the pump primed and going, then I'll test the water to see where it's at.

So, what do you recommend I do first at that point?

From what I've read, I should first put some cyanuric acid in a sock and drop that in the skimmer basket. I'm thinking I should first shoot for a CYA level of 30. I will let the PoolCalculator figure out how much acid to put into the sock. Then I'll add chlorine AS IF the CYA was already at 30. That means a FC level of 4.

Then I'll adjust the TA and pH. My fill water has a pH of 7.7 and a TA of 90. So, I'm thinking that I'll probably have to lower the pH just a little.

[PoolDoc]

If you have access to a Sams Club, I'd buy 2 of their 24# boxes of bagged dichlor. Each 1lb bag will add about 2.5 ppm of chlorine, and 2 ppm of stabilizer (CYA). Once you've reached 60 ppm CYA (= ~30 bags of dichlor, on your pool), you'll want to switch to bleach. Dichlor ALSO lowers your pH, not immediately, but later. So, you'll need some of the borax on hand, to maintain your pH, but since your pH is starting a bit high, you may not need it aft first.

You can also use cal hypo, cautiously. It will add calcium which you will need at first.

However, you need to understand that with a pool in the desert, and with a DE filter, you are going to be constantly losing water to evaporation -- leaving all the minerals behind. And with a DE filter, you will NOT be losing water to backwashing. This means the replace water will ADD to the calcium present.

So, while you want to get your calcium up some now (maybe, 180) you don't want to hurry, and you don't want to go too far, since you'll also be adding MORE calcium every time you top off your water.

[PoolLizard]

If you have access to a Sams Club, I'd buy 2 of their 24# boxes of bagged dichlor. Each 1lb bag will add about 2.5 ppm of chlorine, and 2 ppm of stabilizer (CYA). Once you've reached 60 ppm CYA (= ~30 bags of dichlor, on your pool), you'll want to switch to bleach. Dichlor ALSO lowers your pH, not immediately, but later. So, you'll need some of the borax on hand, to maintain your pH, but since your pH is starting a bit high, you may not need it aft first.

I have a Costco nearby. I still have 11 1 lb bags left from the last box I bought.


You can also use cal hypo, cautiously. It will add calcium which you will need at first.

Still have some of that.


However, you need to understand that with a pool in the desert, and with a DE filter, you are going to be constantly losing water to evaporation -- leaving all the minerals behind. And with a DE filter, you will NOT be losing water to backwashing. This means the replace water will ADD to the calcium present.

Not sure I'm following you here. True, I do have a lot of evaporation, but I also do a lot of backwashing because even though this is a desert climate, my immediate area has a lot of tree leaves and other crud flying into the pool on a regular basis. Ergo, a lot of backwashing/filter cleaning.


So, while you want to get your calcium up some now (maybe, 180) you don't want to hurry, and you don't want to go too far, since you'll also be adding MORE calcium every time you top off your water.

Got it.

[PoolDoc]

Depending on what sort of DE filter you have, and how you clean (open & wash down VS. backwash), and how long you backwash, pools with DE filters tend to actually 'waste & replace' from 10% to 50% of the water that pools with sand filters use. This means that CYA, calcium, metals, etc. accumulate in such pools more rapidly than in pools with sand filters.

Of course, pools with cartridge filters tend to 'waste & replace' even less, maybe 5 - 10% of what pools with sand filters do.

[PoolLizard]

Okay, I just completed a cpmplete test of the refilled pool water. Here are the results:

FC 0.5 (10 ml sample)
CC 0.0
pH 8.0
TA 100
CH 100
CYA <30

So, I guess I'll start adding dichlor now.

[PoolLizard]

At 10:00am I added four 1 lb bags of dichlor to the pool.

At 11:00am the water test numbers are:

FC: 10
pH: 7.4
TA: 100
CH: 90
CYA Not tested. I'll wait until tomorrow to test that again. I'm waiting on my 8 oz bottle of R-0013 to arrive in the mail.

So, looks like I need to up the CH a bit.

[PoolLizard]

Okay, 6:00pm water test:

FC: 5
CC: .5
pH: 7.4
TA: 90
CH: 90
CYA: <30

Gonna add some cyanuric acid. All I have at the moment is 20 oz of hth stabilizer, adding that now, will get more later.

[PoolDoc]

Just a heads up: 11lbs of dichlor into 27K gal should give you 24 ppm CYA. But check the Costco dichlor, and make SURE it's undiluted (55% or 61% available chlorine). If it is, you might want to use the dichlor to raise your CYA, rather than buying CYA.

Dichlor, at $2.50/lb (Sams Club price) = $5/lb as stabilizer without considering chlorine. But hard-to-dissolve HTH (or other brand) stabilizer is often sold at $5/lb or MORE. When you consider that a pound of dichlor has about the same chlorine as a $2 0.75 gallon jug of Walmart bleach . . . using dichlor is a very cheap and easy way to add BOTH chlorine and stabilizer.

The primary CAUTION here is that this applies to pure undiluted dichlor, purchased at a good price. That rules out most Lowes, KMart, Walmart and pool store offerings. It also rules out Costco in MY area, but apparently their stock varies from store to store.

The secondary CAUTION is that this "good deal" ONLY applies while you still NEED stabilizer. Using dichlor, after you have enough, chlorine may be an OK deal, but once your near the "TOO MUCH" level, dichlor is a "bad deal"

[PoolLizard]

My "shock" (Di-chlor) from Costco says this on the label:

ACTIVE INGREDIENTS:
Sodium dichloro-s-triazinetrione.... 58.2%
OTHER INGREDIENTS.................41.8%
TOTAL INGREDIENTS.................100.0%

How do I know if it's UNdiluted dichlor?

I now have an 8 oz bottle of R-0013 reagent, so I'm going to keep testing the CYA level about every other day while I'm adding the dichlor. I don't want to overshoot the target and have to refill the pool again. Taking it cautiously while still maintaining the FC at 7 - 10 ppm.

Is this stuff a good price? Even at their sale price, it seems a little pricey to me.
http://tinyurl.com/l5fk6mv

[PoolDoc]

It's heavily diluted dichlor -- pure dichlor would be:

Sodium dichloro-s-triazinetrione.... 98% (or higher)
OTHER INGREDIENTS.................2% (or lower)
TOTAL INGREDIENTS.................100.0%

If you look, you'll probably find the "available chlorine %" -- I'm guessing it will be in 25 - 35% range, instead of 55 - 61% as it should be.

Here's what I've been posting for dichlor:

PoolBrand granular dichlor 50lbs (http://www.samsclub.com/prod4340004.ip) @ Sams Club => ~$2.50/lb (Jul 2013 in Chattanooga)
PoolBrand dichlor bagged shock 24lbs (http://www.samsclub.com/108822.ip) @ Sams Club => ~$2.50/lb (Jul 2013 in Chattanooga)

Kem-Tek dichlor 22 lbs (http://www.amazon.com/exec/obidos/ASIN/B0030BEHZA/poolbooks) @ Amazon => ~$3.60/lb (Jul 2013)
Kem-Tek dichlor 12 lbs (http://www.amazon.com/exec/obidos/ASIN/B0030BEHZ0/poolbooks) @ Amazon => ~$4.00/lb (Jul 2013)
Kem-Tek dichlor 5 lbs (http://www.amazon.com/exec/obidos/ASIN/B0015UIOWK/poolbooks) @ Amazon => ~$4.50/lb (Jul 2013)
Kem-Tek dichlor 2 lbs (http://www.amazon.com/exec/obidos/ASIN/B0030BEI40/poolbooks) @ Amazon => ~$6.50/lb (Jul 2013)

Nava dichlor Chlorinating Shock 1lb (http://www.amazon.com/exec/obidos/ASIN/B003Z8Z180/poolbooks) @ Amazon => ~$4.99/lb (Jul 2013)

Keep in mind that Amazon products normally ship free; and that in many parts of the country, you will not have to pay sales tax. Shipping + tax can increase the cost from other suppliers by 15 - 40%, so compare delivered cost, not nominal price.

The prices above compare very favorably to 'wholesale' prices. My local SCP (wholesaler) would match the Sams Club price for me if I asked, but I don't, because he'd lose money doing so -- I just buy from Sams, myself.

Pool Water Products is a wholesaler in the S. Florida, perhaps the MOST competitive pool pricing market, with many pool stores selling commercial bleach. PWP's Sept 2013 sales flyer shows per pound prices for dichlor, ranging from $2.65/lb (50#) to $3.40 (12x2# case). As you can see, Sams Club -- selling retail -- is cheaper. Amazon is only slightly more, but if you don't pay shipping or tax for delivery to your location, will be about the same price.

For reference, 1lb of dichlor di-hydrate (55% avail. chlorine) is approximately equivalent to 7/8 gallon of 8.25% household bleach in chlorine content.