Superchlorination

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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Postby chem geek » Wed 19 Dec, 2007 13:36

I forgot to mention that with chlorine combining with ammonia to achieve breakpoint, you won't actually stop at monochoramine. Instead, you can end up with Nitrogen trichloride and that is VERY unstable in sunlight. So sunlight clearly helps with the breakpoint reaction.

As for CYA not building up, that's just B.S. as many pool and spa owners (the later using Dichlor) have measured huge CYA levels well over 100 ppm and this happened in my own pool after just 1-1/2 years of Trichlor puck usage -- and I had a pool cover so was only adding around 0.5 ppm FC per day! But 1-1/2 years is 550 days times 0.5 times 0.6 CYA/FC = 164 ppm. I actually had around 120 ppm due to some splash-out. My pool is 16,000 gallons and I have a cartridge filter, so no backwashing or vacuum to waste.

CYA can break down over the winter if you let your pool go without chlorine as there are soil bacteria that can find their way into your pool and will metabolize CYA and break it down into ammonia. Upon spring opening, it can take a LOT of chlorine to break down that ammonia and you need to add CYA again, but this bacteria breakdown of CYA does not always happen and you certainly cannot count on it.

FC measures both the truly free chlorine of hypochlorous acid (that disinfects) and hypochlorite ion (that does not disinfect) AND the chlorine that is bound to CYA (known as chlorinated cyanurates) because such chlorine is released from CYA in seconds to get measured in the FC test. However, these chlorinated cyanurates are not strong disinfectants and are not oxidizers.

It is true that for SMALL pools (< 10,000 gallons) and regular backwashing that one can keep the CYA level down, perhaps to below 100 ppm. You certainly can see from my calculation how you won't get above around 160 ppm and as you approach that it increases very slowly.

Now I understand why your pool isn't getting algae, which is usually the first thing that happens when the CYA gets high and the FC isn't raised to compensate. You are also adding an algaecide and that helps prevent algae growth. You can certainly keep using that product you have since you've already bought so much. I just wanted to let you know that there are other alternatives if you manage the CYA level. You can use chlorine alone (i.e. chlorinating liquid or unscented bleach) for disinfection and to prevent algae and do not need stabilized chlorine products, algaecides, flocculants or clarifiers, etc. Since you've already bought that in a combo product, you might as well use it.

The Dichlor is a bit more troublesome as it increases CYA even faster than Trichlor (9 ppm CYA per 10 ppm FC for Dichlor vs. 6 ppm CYA per 10 ppm FC for Trichlor), but again, since you've already bought it, just make sure you continue your vacuum to waste program to keep diluting your CYA level.

If you have a plaster pool, then you should be aware about a possible side effect of high CYA levels as described in this link .

Richard


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Postby chem geek » Wed 19 Dec, 2007 13:41

sparkwatercleaner wrote:Another question:

If CYA is too high and I therefore need to keep a higher FC level in my pool, will it cause any problem as it is higher than normal??? For example, If my pool demands 6ppm FC because CYA is too high, would it be the same as 6ppm FC with no CYA??? (I ask beacause the harm it may do to swimmers)

First off, with an algaecide as you are using, you don't need to increase the FC level as much. Secondly, it is the disinfecting chlorine level that determines the rate of oxidation of skin, hair, irritation to eyes, etc. This means that roughly speaking it is the FC to CYA ratio that matters. A 6 ppm FC with 100 ppm CYA is technically the same disinfecting chlorine concentration as 0.05 ppm FC with no CYA. Yes, you read that correctly and it explains why indoor pools at 1-2 ppm FC with no CYA are so irritating. My wife complains about this every winter season when she must use a community center indoor pool where her swimsuits degrade (elasticity in rubber gets shot) in just one winter of use while in our own outdoor pool her swimsuits show no such degradation and only slight wear after 4 seasons of summer use. She also complains about her skin getting more dried out and her hair more frizzy when using the indoor pool over the winter. My outdoor pool has around 3.5 ppm FC with 30 ppm CYA (but I have an opaque pool cover so can keep the CYA level lower).

The only time that the absolute FC level would matter would be in terms of the total amount of chlorine available as CYA is like a chlorine buffer holding chlorine in reserve. So the RATE of reactions is slower due to CYA reducing disinfecting chlorine concentration, but the higher FC means there is more CAPACITY or amount of chlorine available to be released over time (so the slower reaction can occur with a larger volume of substances). So drinking water with the higher FC would have more of an effect, but you'd have to drink a heck of a lot of pool water before there would be any problem -- and you don't normally do that anyway. If you don't rinse your swimsuits off after getting out (or taking them off), then it's possible for them to have more reaction -- it will be slow, but there's more chlorine for reaction (assuming it doesn't just outgas first). My wife always rinses her swimsuits after using the pool (both the indoor and outdoor pool situations) so the degradation with the indoor pool water had to do with the reaction rates due to no CYA, not to the FC level (which was lower than in our outdoor pool anyway).

Richard
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Postby sparkwatercleaner » Wed 19 Dec, 2007 18:25

Thank you Richard for all your valuable help.
FC has dropped around 4-5 ppm since last night to now (evening). So, CYA may be around 30-80 ppm right? I think there is no algae or other source which may be consuming FC. Do you still think I should dilute my pool water (the pool is 1 year old, never drained it)???
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Postby chem geek » Wed 19 Dec, 2007 19:19

If it's only been one year and with the dilution you've been doing, I would guess that your CYA is under 100 ppm so I'd just leave it as is as far as that goes. The real question is what to do going forward. If you used unstabilized chlorine, such as chlorinating liquid or unscented bleach, then you wouldn't build up any more CYA. Since you want to continue to use what you've bought, about the only way to keep the CYA constant is to drain enough to compensate for the amount added.

If you know the weight of your pucks (3" pucks come in 6,7,8 ounce weights) and you know how often you add a puck to your pool then with the 10,000 gallon volume I can estimate how much FC and CYA you are adding each day. So I can tell you roughly how much you need to dilute each week to maintain a stable CYA level that at least is likely to be below 100 ppm which you can probably live with given the algaecide in what you are using.

Richard
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Postby sparkwatercleaner » Wed 19 Dec, 2007 22:59

Well, I add 2 tabs/pucks to a floater each week. They are 7 ounce tabs/pucks (200 grams, actually). The test kit reads almost 1 ppm FC at any given moment I test. I also add almost 3 ounces of granulated (dichlor) chlorine weekly, as my pool shop recommends me to "reinforce" the chlorine added by the pucks/tabs.
Do these tabs have the same amount of trichlor as normal trichlor tabs?

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