When to Shock

What is floc, clarifier, stabilizer, cyanuric acid,
algaecide, brightener, dichlor, sodium hypo,
sodium bisulfate, ....??
Denniswiseman
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When to Shock

Postby Denniswiseman » Sun 16 Oct, 2011 11:51

Most of the reading I have come across says to shock weekly or fortnightly
Surely it should be how much the pool is being used.

I tend to use my pool every day for about 30 minutes which equals about 3.5 hours a week
Should I still shock weekly/fortnightly


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When to Shock

Postby czechmate » Sun 16 Oct, 2011 19:24

There has to be a whole slew of opinions on this subject. Kind of like "how often to use an algecide".
Go into archives and read Chemgeek's comments on the subject.
Sure, it depends very much on the conditions (pitting and cracks)of the plaster where algae can hide invisible and wait for your slip-up to take over.
I have not shocked my pool once, this whole season. Neither I have used 1 ounce of any algecide.
My CYA is 100 and CH 760. Even with these bad numbers, I was able to keep the algae at bay by lower PH and correct TA and by computing my CSI twice a week prevent the potential damage to the plaster.
(The reason I did not drain 65 % is really stupid. I did not want to loose my 30 ppm of borates and 2300 ppm of salt).
With a smooth clean plaster, by my own experience shocking is not necessary.
Provided you have the time and discipline to maintain FC level relative to CYA.
(Sure, there are instances where you may want to shock, in a case of accidental introduction of waste in the pool or bad storm that puts a dirt and decayed organics in your water).
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When to Shock

Postby chem geek » Mon 17 Oct, 2011 01:37

A pool properly managed and maintaining an appropriate Free Chlorine (FC) level relative to the Cyanuric Acid (CYA) level does not need to be regularly shocked. Bather waste is continuously being oxidized by chlorine that is maintained in the water. The primary reason the pool industry promoted regular shocking was to make up for the fact that the continued use of Trichlor tabs/pucks built up the CYA level making the chlorine less effective. Rather then have you simply raise the FC level proportionately to keep the active chlorine level constant, they recommended weekly shocking as well as use of (high profit margin) algaecides.
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When to Shock

Postby Denniswiseman » Mon 17 Oct, 2011 04:31

Thanks for that info czechmate & chem geek, we all tend to do as we are told by the manufacturers (if we don't know better)

My pool is fibreglass and covered so there is no plaster or UV problem
I was using stabilised chlorine untill my CYA went sky high. After multiple partial drains and refills the CYA is under control. I now use Fi-Clor Superfast Granules which I broadcast 200gm straight into the pool every 1.5 days (very simple).
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When to Shock

Postby chem geek » Mon 17 Oct, 2011 15:00

The Superfast Granules are 75% Cal-Hypo. Though it will not increase Cyanuric Acid (CYA), it will increase Calcium Hardness (CH). For every 10 ppm Free Chlorine (FC) added by Cal-Hypo, it will also increase CH by at least 7 ppm. So if you are using 2 ppm FC per day of chlorine, then you will be increasing CH by at least 42 ppm. The good news is that if your fill water isn't high in CH, then you could probably go an entire swim season without a problem, especially for your fiberglass pool since it doesn't need the full saturation of calcium carbonate all the time. However, you would need to dilute the pool water between seasons, perhaps using winter rains to overflow/dilute.

Ideally, you would use something like 12.5% chlorinating liquid or 6% bleach, but that may not be as available to you. For example, you can get Crown 14-15% chlorinating liquid at AquaPools&Leisure , but with delivery that could get expensive. Remember that you can use The Pool Calculator to calculate dosages.

Basically, it's easiest to maintain water balance using primarily chlorinating liquid or bleach, but Cal-Hypo is next best as the buildup in CH isn't as fast in percentage terms to when it would be a problem compared to stabilized chlorine (though in areas where the fill water is high in CH it isn't something to use regularly) while the worst is stabilized chlorine such as Trichlor and especially Dichlor as they build up CYA fairly quickly unless there is significant water dilution. Of course, Trichlor pucks/tabs are convenient and avoid the every day or two dosing, but such convenience comes at a price of needing to either dilute a lot to keep CYA in check or to raise the FC level higher as the CYA rises or to use supplemental algaecides or phosphate removers to try and prevent algae growth.

Note that when using Cal-Hypo, you should pre-dilute it in a bucket or if you find it dissolves reasonably when added to the pool directly then lightly brush the side and bottom of the pool in the area where you add it to ensure thorough mixing. Adding concentrated chemicals slowly over a return flow with the pump running usually disperses the chemical reasonably well.
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When to Shock

Postby czechmate » Tue 18 Oct, 2011 09:36

If you choose to add granular chlorine directly in a skimmer make sure the pump will run for a minimum of 1hour after that. I still do not think it is safe for the DE elements, where you may have a some bare spots exposed to the high chlorine. These wiIl sometimes occur during bump backwash.I learned this the hard way and it cost me 250.00 on the new elements. Of course if you can't install these yourself, the price will double. On the sand filter it is a safe procedure, though.
For me it works best when I deposit the Cal-Hypo from a cup slowly around the perimeter to slide on the walls and provide high concentration wher algae may be trying to start. After 30 minutes I turn on the pump and the Polaris poolsweep without the bag.This will ensure nice mixing and cleaning, without damaging the bag by entraped chlorine granules.
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When to Shock

Postby Denniswiseman » Sun 11 Dec, 2011 14:40

Hi there

Thought that I'd let you know

I've purchased some 14- 15% sodium hypochlorite and have been dosing at 290ml per day to maintain 3ppm
The 20 litre drum should give me 69 doses which works out at 34p a day not expensive at all

I was a bit apprehensive at first but I decanted the drum into 20 x 1 litre bottles and measured out from there to pour in over the returns
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When to Shock

Postby chem geek » Sun 11 Dec, 2011 18:06

That sounds great. Over time you should be able to get an idea for your typical daily chlorine usage and you could dose with a larger quantity less frequently if that is more convenient. However, the lowest overall amount would occur from the daily dosing. If you are able to use a mostly opaque pool cover, you should find that your chlorine usage drops considerably. Even though I keep my pool at around 88ºF (31ºC) in the summer, I have an opaque pool cover so my chlorine usage is no more than 1 ppm FC per day in spite of the pool being used 1-2 hours every day. For a warm residential pool that is kept open and exposed to sunlight, typical chlorine usage is 2-3 ppm FC per day.
Denniswiseman
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When to Shock

Postby Denniswiseman » Mon 12 Dec, 2011 05:53

When I checked the chlorine on Saturday it was 3ppm
I am now going to try 200ml a day and check again on Wednesday
Daily dosing is OK with me, I have a thick thermal cover and the pool is covered so I have no UV problem
1ppm drop daily is what I'm experiencing

88ºF (31ºC) is what I like to keep my pool at if possible but we heat it by a 5 kw heat pump and the cooler temperatures aren't beneficial to the operation albiet in the summer we get solar gain from the greenhouse effect and hardly have to use the heat pump at all. This morning it was 28ºC and it may raise 1ºC during the day which is the amount it drops through the night.

It's good to bounce what we are doing of professionals like yourselves. It tends to make us experts as well.

Keep up the good work it's much appreciated

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