Mid summer algae and polyquat

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Backyardchemist

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LifeTime Supporter
Jun 2, 2010
31
Northern Vermont
Hello everyone,

It's been a great summer so far using the BBB method on my pool. Overall it's been crystal clear, and this year the polaris filter is even working properly so I no longer have to dive for acorns.

Unfortunately during a heat spell a couple of weeks ago I let the FC dip to 2-4 FC for a few days which prompted an algae bloom. After a few days of progressive cloudiness and green hue (slight) I followed the pool school rules on shocking and am gaining ground.

Here's my dilemma: It seems that my CYA has been on the high side all year (in the 50 ish range). Aside from an initial dose of dicholor packets (with the CYA) at opening in early June I have not added anything but straight bleach to the pool. As a result I seems I have to keep the FC to 6 or above to keep the blooms at bay, which for a 25k pool is a bit of bleach to haul.

As a result I'm wondering your thoughts on adding in weekly polyquat doses. With this since it's mid summer and the pool is open how much polyquat 60 do you recommend I add for an initial dose. After that what do you recommend that I add for a weekly dose.

Ultimately I'd like to be able to keep the FC in the 3-4 FC range ... will adding polyquat regularly help me to do this?

Thanks!

FYI my current #'s are:

Appearance - slightly cloudy
FC=23 (@ shock level for recent bloom - still shocking because I lost 2.5ppm last night)
CC=0
PH=7.5
TA=90
CYA=50ish
 
Re: Mid summer and algae and polyquat

will adding polyquat regularly help me to do this?
Click to expand...
No. You could lower your CYA through a drain/refill process down to around 30 or so but it may have little overall effect on how much bleach you have to haul.

AS an alternative for next year, you could start using pucks from the beginning of your swim season (watch your pH) and stop using them as your CYA approached 40-50. You would then only have to haul bleach for a month or two, perhaps.
 
Re: Mid summer and algae and polyquat

Lowering your CYA level will mean adding more total chlorine/bleach to the pool every day. CYA protects chlorine from sunlight so well that you actually lose less chlorine to sunlight despite the higher FC level. If you want to cut back on the amount of chlorine you need to add each day you could try increasing your CYA level a little.

polyquat can reduce the amount of chlorine you need to add in a few cases, but most of the time it won't have any obvious effect on chlorine usage. Dosage instructions are on the bottle.
 
Re: Mid summer and algae and polyquat

I never understood why people equate the level they keep their FC at with the overall amount of bleach they use. Regardless of the target level, the amount of bleach used has much to do with the daily chlorine loss and little to do with the actual level. If your pool loses 2ppm per day you use the same amount of bleach if it falls down to 7 and you bump up to 9, as if it falls down to 3 and you bump it up to 5.

If you feel like you are going through a lot of bleach, it probably has to do with the fact that algae was allowed to take hold and which is causing increased daily chlorine loss.

Lowering your CYA probably isn't the answer because more chlorine will be burned off by the Sun, thereby increasing your daily chlorine loss (and shoulder pain).

Polyquat may provide some insurance against an algae bloom, but is not a substitute for maintaining sufficient FC (sanitizer) for you CYA level.
 
Re: Mid summer and algae and polyquat

Thanks all for the feedback on the CYA vs. FC trade off. I've been confident about the FC levels I've been maintaining, recent bloom aside, and you are right that increasing 2 ppm is the same amount of chlorine when raising from 2 to 4 as when raising from 3 to 5.

My original consideration was could I maintain a lower FC with my CYA by adding polyquat AND not have to fight algae blooms with bulk purchases of chlorine from the hardware store (the aforementioned lugging). Pucks may be the ticket going forward especially if I keep an eye on PH and CYA as suggested.

Also, thanks for the thoughts on polyquat 60 doses ... with the BBB approach I've become fairly skeptical of pool chemical labels, so it's good to hear that the recommendation on the polyquat bottle is a fine metric.

One more question on the polyquat ... I've gone ahead an added an initial dose, but I've been unable to find information on 'safe swim time' following addition. How long should we wait before swimming after adding the polyquat?

Last, I know there is a wide range of opinion on FC levels and 'safe swimming.' I have yet to find a good account of how high is too high. The CDC says that 5 is the recommended FC level for public pools, but I imagine in practice this terrifically low. Do you have any recommendations on safe vs. unsafe FC levels?

(My boy is coming home from Boy Scout camp tomorrow and he'll want in!)

As always, thank you for the terrific information!
 
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