Calcium Hypochlorite damaging to fiberglass?

[jackj]

I recently switched from sodium hypochlorite to calcium hypo for shocking, but now when I went to the pool store they said that fiberglass shouldn't be treated with calcium hypo because the % of free chlorine is so high it will damage the fiberglass. For that matter, they said, they also don't recommend the liquid shock, sodium hypo, because until it's adequately diluted it has a similar effect. They (of course) sell a product, Chlor Brite, which is Sodium di-chloro at 52%, vs. the 73% of calcium hypo. I suggested that only using 2/3 to 3/4 of a bag of calcium hypo would equate to the 55% full bag of the Chlor Brite, but they said that it still causes the hyper-chlorination that damages fiberglass.
I now checked the Leslie's (oops, said it!) website, and they say that their Cal-hypo is safe for all pool materials, and that it's the fastest dissolving Cal-hypo available. But they do also mention under the benefits of the Chlor Brite that because it's fast dissolving and pH-neutral, it won't damage vinyl or fiberglass, which could happen if a product didn't dissolve well or were more acidic. Sounds logical, anyway. Except don't most shocks raise the pH - indeed, their Cal-hypo says it's got a pH of 11.2, which makes them base, no? I guess that could damage, too, but the website said more acidic than 7.0 (Chlor-Brite).
Could someone please clarify any/all of this?! I can't wait to be able to afford a SWG...

 

[PaulR]

One of the more chem-aware gurus will correct me but my memory of the different chlorine types is that hypochlorites are net pH neutral and dichlor/trichlor are net acidic. The hypochlorites have high pH but the chlorine reaction is acidic so you net very little change in pH.

Whatever powder you use, if you dissolve it in a bucket and pour it slowly in front of a return, it's not going to damage the fiberglass. (Advantage of liquid chlorine/bleach: no dissolving required.) Whatever powder you use, if it sits on the bottom for a while, it could do damage.

(You have some particular reason to switch to cal-hypo? Some particular reason to shock, for that matter? If you're conscientious about maintaining your FC level there's generally no need to shock.)
--paulr

 

[chem geek]

Welcome to TFP!

(I wrote this while Paul was posting so some info is duplicated. He is correct about the net pH neutrality of hypochlorite sources of chlorine though they do raise the pH upon initial addition and then drops as the chlorine gets used up.)

You can learn more about different sources of chlorine by reading some of the Definitions and Abbreviations in the Pool School.

Cal-Hypo is usually pre-dissolved in a bucket of water because it tends to not dissolve that quickly. Dichlor dissolves better, but not always completely. However, any concentrated source of chlorine can be damaging if not thoroughly mixed with the water so one generally adds the chlorine by pouring slowly over a return flow in the deep end with the pump running. If properly added and mixed, the chlorine will not be damaging to pool surfaces.

The following are chemical facts for some chlorine sources independent of concentration of product and of pool size:

For every 10 ppm Free Chlorine (FC), Trichlor also increases Cyanuric Acid (CYA) by 6 ppm.
For every 10 ppm FC, Dichlor also increases CYA by 9 ppm.
For every 10 ppm FC, Cal-Hypo also increases Calcium Hardness (CH) by 7 ppm.

So shocking with Dichlor will increase CYA quite rapidly. Higher CYA levels make chlorine less effective so one should generally never use Dichlor for shocking unless one has very little CYA to start with. Cal-Hypo is OK if the CH is low, but generally chlorinating liquid or bleach is best.

Why did you switch from sodium hypochlorite to Cal-Hypo?

Richard

 

[JasonLion]

Any form of chlorine can damage the pool surface if used incorrectly. When used correctly, no form of chlorine will cause any damage. You don't want any tablet, powdered, or granular chlorine product sitting on the bottom of the pool. Likewise, you don't want to pour a liquid chlorine product directly onto the the fiberglass. If you pre-dissolve the solid products and pour everything slowly in front of a return jet while the pump is running there won't be any damage. There are other factors, which PaulR and chem geek have already covered, that determine which product is the best choice.

 

[jackj]

Thanks much, guys! So, is fiberglass more susceptible than other surfaces, though? Not concerned, as long as I follow your advice. Just wondering if the guy was right about that aspect.
The reason I switched to chlor-hypo was because it was cheaper (I haven't compared with store-bought bleach), and I periodically have to add calcium anyway, so figured that was just a bonus. And I was also told that my TDS was high bec. of using the liquid sodium-hypo, though from my reading I don't think that's an issue. Or is it? I figure, how much TDS must a salt pool have?! Finally, it's more convenient not having to get jugs every week. On that note, is it true that the jugs of chlorine lose their potency in a week, so 2 or 3 isn't an option?
The reason I shock is because I'm not convinced I'm keeping FC levels up consistently. I've always used tabs, but after getting very high cya and consequent algae problems (and after reading here, realizing that and dealing with it adequately), I've gotten stingy with the stabilized tabs. But still use them for my day-to-day chlorination; just reduced.
And other suggestions?
Thanks for the great forum!

 

[JasonLion]

I wouldn't say that fiberglass is more susceptible. Each kind of surface reacts to chlorine damage in different ways.

Cal-hypo is convenient, as long as you actually need the calcium. But if your calcium level gets too high there can be serious problems. That doesn't usually happen right away, but it is something you do need to keep an eye on.

Don't worry about TDS at all. It is a very misleading measurement that doesn't tell you anything interesting. Long ago, when there wasn't a test for CYA, people used TDS measurements as a proxy for the CYA level. But now that CYA can be measured separately, there really isn't any point in thinking about TDS.

Household bleach will last about 6 months if stored in a cool dark place. Liquid chlorine, which is the same thing, but with a higher concentration of chlorine, will last about one month if stored in a cool dark place. Both kinds will degrade much more quickly if they are stored somewhere that gets very hot.

If you don't already have one, getting your own top quality test kit is the single best thing you can do to get better control over your pool and save money on chemicals.

 

[chem geek]

(I posted this while Jason was writing. He's more conservative in the bleach and liquid chlorine life, but that's fine and is still in the ballpark.)

Other than for metal staining, I wouldn't say that fiberglass is more susceptible than other surfaces. Each has their own issues. For metal staining, fiberglass is most susceptible, than plaster, and least is vinyl. For being able to handle either low pH or high FC levels (i.e. a Trichlor puck or Cal-Hypo chunks on the surface), vinyl is most susceptible, then fiberglass and plaster are comparable unless the exposure to low pH is longer in which case plaster may be worse than fiberglass (speculation on my part).

It's fine to use Cal-Hypo as a source of chlorine if your Calcium Hardness (CH) is low. Just keep in mind that for every 10 ppm Free Chlorine (FC) added by Cal-Hypo, it also increases Calcium Hardness (CH) by 7 ppm. So the CH will build up over time and this can lead to scaling.

With continued use of Trichlor, the Cyanuric Acid (CYA) will build up over time and this makes chlorine less effective so algae can end up growing faster than the chlorine can kill it. For every 10 ppm FC added by Trichlor, it will increase CYA by 6 ppm. Even at a low 1 ppm FC per day from Trichlor, this is over 100 ppm of CYA added in 6 months.

As for TDS from bleach, ALL sources of chlorine increase TDS, specifically salt (sodium chloride, assuming you adjust for pH from various chlorine sources). For every 10 ppm FC, ALL sources of chlorine result in at least 8 ppm salt because the chlorine gets used up to become chloride. For chlorinating liquid or bleach (or lithium hypochlorite, though that is VERY expensive), these sources of chlorine add an additional 8 ppm salt upon addition so for these sources the net result is that for every 10 ppm FC they increase salt by 12 ppm. However, this is no big deal because even at 2 ppm FC per day chlorine usage, this is an increase of around 430 ppm salt in 6 months. As you point out, a saltwater chlorine generator (SWG) pool has 3000 ppm so the increase in salt from chlorine use is not a big deal and the water is rather easily diluted.

When comparing the side effects of chemical additions, it is the percentage of increase in the extra component that is relevant. For 2 ppm FC per day over 6 months, Trichlor would increase CYA by over 200 ppm so even at the highest recommended level of 80 ppm this is an increase of at least 250%. If Cal-Hypo is used, this would increase the CH by over 250 ppm which at a 300 ppm CH level would be an increase of 83%. For chlorinating liquid or bleach, the increase of salt of 430 ppm compared to a 1500 ppm TDS level is an increase of 29%. Dilution from splash-out, backwashing, rain overflow can readily handle the salt increase to keep it in check. It might handle the CH increase depending on how much dilution there is, but it is very unlikely to handle the CYA increase.

Jugs of chlorine do not lose their potency in just a week or two. Bleach stored at room temperature will last for a year or more. 12.5% chlorinating liquid will last for 2 months or more unless stored at higher temperature. See the chart at the bottom of this link to see the half-life of chlorine at various concentrations and temperature (half-life means how long it takes to lose half its potency).

You can certainly shock if you want to and can use a mix of chlorine sources as well. It's your pool and you can do whatever you want. Just keep in mind that shocking is not necessary if you maintain the appropriate FC/CYA level. Also just keep in mind that the CH and CYA will increase from your use of Cal-Hypo and Trichlor, respectively. So long as you understand that and keep track of it and adjust accordingly, then you are in control of your pool (rather than the other way around). You could even use extra products at extra cost if you wanted to prevent algae even when the chlorine got too low, but again that is unnecessary. Probably the least expensive safe approach for such "insurance" would be to use 50 ppm Borates in the pool.

Richard

 

[jackj]

Boy, thanks both of you for the great feedback! Such a wealth of info.... Particularly re: the history of TDS and why it's tracked, and at one time WAS a concern. One pool employee, who actually seems knowledgeable and even said she'd attended a seminar from someone here, or from the other pool forum, still believed that TDS acted as a barrier between the chlorine (and other chemicals?) and the algae.
So, now that I don't fear that the chlorine jugs will go bad in a week (and since they had a buy 2 get 1 free deal), I've got three jugs, stored in my laundry room at room temp.
Unfortunately, now, of course, I have a new problem. My TA was low, and so I added baking soda. And though I added less than what "should" have been called for, it shot my TA up to 170! pH is 7.6. Perhaps their test was off, either the too low or now the too high one (I know, get a test kit!) I read the sticky on lowering TA, so off to buy acid and some kids to jump in. Ooh, or maybe put my wet-vac on "blow" and stick the hose underwater?
And, not sure if it's related to the TA, but when my TA tested 170, my FAC said 5 (hadn't shocked), yet the next morning I had hints of algae. Shocked that night, and still the next day! So, now I did again, still some algae? in the bottom, so I wet-vac'd it out and dumped it, and cleaned the filter. At first I wasn't sure if it might be cal-hypo that had settled, but the color, and the fact that I hadn't used the cal-hypo in a week, made me pretty sure it was algae. Hopefully, got rid of it now. And plan on comparing prices on the bleach vs. jugs (my calcium is in range now), and perhaps just adding that daily to maintain, since my cya is already at 50, too. Oh, how I want a swg...
Thanks again for all the help and the great forum.

 

[frustratedpoolmom]

High TA is only a problem if it causes the PH to drift up to 7.8, and the frequent acid additions become annoying. So the "lowering TA" article just tells you how to speed up the process.

Everytime it creeps up to 7.8, you can simply lower the PH down to 7.2, and the acid will lower the TA too, eventually both will be in the recommended range.

But you need your own test kit to monitor these levels appropriately, plus your own testing will be more reliable.

With your own test kit, you can do an overnight loss test to confirm if what you are seeing, is in fact algae.

Proper testing takes all the guesswork out of owning a pool.
http://www.troublefreepool.com/pool-school/pool_test_kit_comparison

 

[jackj]

Thanks for the tips. I had more "algae" this morning, though it's just along the same path on the bottom, my guess is due to settlement and the circulation of the water. I don't have the pool vac in now. So, I sucked it up again (and there was less, at least), figuring even if it's undissolved cal-hypo I don't want it on the bottom. I saved the second bucket, to let it settle out again, while I took TWO water samples to the pool store. And my chlorine came back as still 5, with a cya of 40, so I'm thinking if it is algae, it would be killed, right? And not green? That's several days keeping it at 5, as it's been 1.5 days since I shocked it for the second night in a row, with floating tabs, too.

So, the samples, tested by the same person (I told her I was watching a neighbor's pool), came out with these discrepancies. FWIW, I said that the other pool was slightly smaller, 16k vs. my 17k. Though, if anything, that should make those readings higher, right? The results:
17K based on 16k
FAC 5 5
pH 7.6 7.6
TA 150 130
Calcium 230 170
CYA 40 40

Now, she's the one who tested my high TA the other day, and I thought she was new, so was suspect, though it turns out she worked at a diff. store for the last year. But with diff. aged reagents, quick, not-precise measuring, I'm not surprised with wrong results. Though here, the only variable would be her techniques.

I won't be doing anything with the calcium at this point; I do have a few bags of cal-hypo left that I'll use next week maybe. I priced bleach at walmart, and it was more than the jugs, though. $2.54 for 1.42 gallons of 6%; Jugs are $4.60 for 2.5 gallons of 12% (I believe; over 10%, anyway). I picked up some Borax as it was right next to it, for future possible use, though it sounds as though unless my pH gets above 7.6 I shouldn't need to lower it with a bunch more acid.
I've got a bit of old liquid acid I'll throw in, since I am at the high end of the pH and do have high TA - it's not a lot. And re-test and see where I'm at. Not sure why, but I've had this acid for 7 years and only needed it a couple times? Guess I'll go to dry then if I need more, though not unless the pH gets to 7.8, right? Any best place to get that, or is the pool store as cheap as any place?

I just checked the wet-vac water, and can't see any settled stuff, likely because in the pool it was all channeled along that line. Now it's more disperse. The water is cloudy, but that's all I can tell.

Now, 2 hours later, I notice the same pattern of green forming in the bottom of the pool, same location, and also a few bits on the stairs, which I was able to reach. Upon trying to touch it, just poofed up and drifted/dissolved- doesn't appear to be cal-hypo, and does appear to be algae. Also, is it helpful at all to vacuum what I'm able to up and throw it out? More just appears to come back, I presume because it's not being killed? So, if I get the chlorine up enough, it will just kill what I leave in, anyway, so no real benefit to sucking it out? And I would've thought that it would've been killed at a constant 5 FAC - plus some, I'm sure, when I shocked it - for several days with a 40 CYA? The calculator says with a 40 maintenance is a 5, though... Guess I'll pull the tabs to try to get cya lower, and continually add chlorine. Unfortunately, don't have access to a FAS-DPD test to confirm how high I'm getting chlorine.
Okay, just read that the pool store CYA tests aren't accurate (though at least it was consistent! Great....

 

[frustratedpoolmom]

With your own test kit, you can do an overnight loss test to confirm if what you are seeing, is in fact algae.

Proper testing takes all the guesswork out of owning a pool.

Your shock level for a CYA of 40 is 15/16. Not 5. At 5, you might stay slightly ahead of it, but you won't kill it.

 

[jackj]

Thanks. Yeah, 5 was the highest the non-fas-dpd could read, but since it was at least a 5 a day and a half after shocking for two days in a row, that likely I was in the appropriate shock range for a 40 cya reading overnight for the two nights I shocked it. I was using the (at least) 5 reading as my maint. for the last few days, and while I shocked overnight, per the Pool Calculator, it should've been up to 20 or so (though not necessarily maintained). Guess I gotta splurge for at test kit...