When to shock

Chlorinating, maintaining the right chlorine levels,
chlorine problems. Dichlor, trichlor, cal hypo, bleach,
granules, chlorine pucks and chlorine sticks.
chem geek
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When to shock

Postby chem geek » Thu 21 Jul, 2011 12:07

czechmate wrote:Your demand on FC will drop to half of todays (4.5 instead 9 ppm) and save you money daily.

That isn't true if one maintains an FC that is proportional to the CYA level. The FC drop with an FC of 6.8 ppm with 90 ppm CYA is lower than with an FC of 3.4 ppm with 45 ppm CYA (see this post for an experiment that shows this). Though at a given CYA level the amount of chlorine lost from sunlight is proportional to the FC level, higher CYA levels protect chlorine from sunlight more through additional mechanisms such as shielding lower depths from UV (i.e. not just from binding to chlorine itself). So having a higher CYA level often results in somewhat lower chlorine usage in spite of the higher FC level needed to prevent algae growth. This is the main reason why 80 ppm CYA is the recommended level for SWCG pools even though the 4 ppm FC is higher than 2 ppm FC with 40 ppm CYA. It is to lower the absolute chlorine loss (FC drop) to reduce SWCG on-time which reduces hydrogen gas bubble generation and associated carbon dioxide outgassing as well as any undissolved chlorine gas outgassing. This reduces the rate of pH rise in SWCG pools.


bnairb
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When to shock

Postby bnairb » Fri 22 Jul, 2011 10:06

So I understand I need a lot more chlorine at 90ppm cya. So today I decided to do a partial drain/fill to get the level down to reasonable. According to what you said and the calculations I've done I need to drain about 3' which should be roughly half or 10000-14000 gallons. In working on this, I have discovered a pink slime inside the skimmer that I've never seen before. I attached a picture. In briefly looking on the net, I've read that red/pink is a bacteria and not a true algae. I've never had this before, but I've never had this cya prob before so I'm only guessing that, as you've explained, my chlorine level is not high enough in relation to the high cya this year to combat the bacteria. I have not had an algae problem, but I attribute that to using Pool Perfect+Phos free to keep the phosphates out of the pool, so to me it makes sense a bacteria would grow but not an algae. I hate to start the red/pink algae? in another post as i'm sure it's related to this chlorine/cya issue.

So, what is it?
Once I get the pool refilled, chemicals balanced, do I need to do something special for this red stuff?

Also, until I can afford a SWG(maybe next year), how much water per week do you think i need to backwash/refill to keep the cya in the tablets from building back up this season?
Attachments
PINK POOL SKIMMER resized.jpg
PINK POOL SKIMMER resized.jpg (151.88 KiB) Viewed 2232 times
chem geek
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When to shock

Postby chem geek » Sat 23 Jul, 2011 01:23

It's hard to tell if that's pink algae. Is it slimy? If so, then it's likely to be pink algae or some other bacterial biofilm. You can add bleach directly to the skimmer during some chlorination and can wipe it with a scrub sponge. Once you start maintaining normal chlorine levels, it should get killed off though if biofilms are present elsewhere (such as in pipes), then you may need to get to shock levels for a while or use a biofilm-breakup product. Unfortunately, there's not enough info to be definitive about the best product to use nor if any of them absolutely work reliably, but as described in this post the Aquafinesse pool tablets did seem to help in this one situation. That's not enough to make a recommendation (we usually wait until we see consistent results from many users), but there's not much else to go on. Again, usually shock levels of chlorine work for pink slime and regular maintenance levels with an appropriate FC relative to CYA keep it away.
bnairb
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When to shock

Postby bnairb » Mon 25 Jul, 2011 05:20

New problem, see viewtopic.php?f=21&t=10471 . Pool water yellow after refill and shock.
Lindon
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My Pool: Outside, in ground, vinyl liner with 'hopper'shaped 7' deep end. Solar covered. L=30' x W =15' (approx. 14.000 imp. gallons.) Sand filtered, outside gas boiler heated to 28C in season. FROG mineral cycler. 3/4hp pump. Tap water is TA= 138ppm, PH=7.1 Ideally like to see pool reading CYA = 40ppm, CL = 1.5ppm, TA = 100ppm, PH = 7.7. Test kit is AquaChek digital analyser & 3 way test strips(PH,TA,CL) plus test strips for CYA.
Location: England

When to shock

Postby Lindon » Tue 26 Jul, 2011 10:45

Fi-Chlor are marketing tubs of slow dissolving CYA free 'Supercapsuls' each with its own special wrapper which is not removed & which they say should be placed in the skimmer basket. The wrapper is supposed to ensure an equal amount of water flows over the capsules surface area & dissolve at equal rates They claim they can be used in previously stabilised water & also in conjunction with stabilised tablets if necessary providing the pool is not dosed from the same place. I've not used them yet but hoping this may be the answer.
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Re: When to shock

Postby paulbest » Wed 10 Aug, 2016 23:06

Shocking your pool is a great way to remove organics in your water, kill off algae, and be sure your pool stays clear during the swimming season. However, when you shock a pool, you essentially limit the time you can use it as you must wait for the chlorine levels to drop to 3-4 ppm before it is safe to swim.

If you keep your pool at the proper chemical balance, you won’t have to worry about shocking your pool. But if your pool’s chlorine levels drop too low, you will need to shock your pool to raise the chlorine levels to ensure a safe swimming environment.
Denniswiseman
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Re: When to shock

Postby Denniswiseman » Thu 11 Aug, 2016 12:48

You can swim up to the correct shock level relative to your CYA if your FC is holding http://www.troublefreepool.com/content/128-chlorine-cya-chart-slam-shock

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