Do you SLAM as soon as you have some algae?

[Pierrot]

Hi all,

I have some algae that show up after a few days. It's on the wall in the shaded area of the pool, yellowish-greenish.

So far it's not a major issue. I just need to brush them off once a week and that's pretty much it. So going through the SLAM process seems a bit overkill. So my question for the community is: do you go ahead and SLAM as soon as you discover some algae, or is it just normal to just brush them off once a week?

CYA: 70
FC: between 5 and 7ppm,
pH: 7.7

 

[kul]

The sooner you Slam the faster it will go. Algae is not routine; it’s caused by low chlorine. Don’t wait for it to get out of control.
Overnight Chlorine Loss Test
SLAM Process

 

[.ben]

I’ve never had algae. I imagine I would SLAM immediately if I ever did.

Algae is not inviting for me to swim at all

 

[Bperry]

Hi all,

I have some algae that show up after a few days. It's on the wall in the shaded area of the pool, yellowish-greenish.

So far it's not a major issue. I just need to brush them off once a week and that's pretty much it. So going through the SLAM process seems a bit overkill. So my question for the community is: do you go ahead and SLAM as soon as you discover some algae, or is it just normal to just brush them off once a week?

CYA: 70
FC: between 5 and 7ppm,
pH: 7.7

Not normal to have to brush off algae.

 

[Pierrot]

Got it. Follow up question then

If I raise the FC to 28ppm (SLAM level when CYA is 70), how many days before FC goes back to 5? Right now I'm losing about 1ppm per 24h. So will it take 23 days, or is the FC daily loss higher when its concentration is higher?

 

[proavia]

Post a full set of test results from one of the recommemded test kits.
Test Kits Compared

FC
CC
pH
TA
CH
CYA
Salt (if a SWG pool)
Water temperature

Do an Overnight Chlorine Loss Test, followed by the SLAM Process if you fail the OCLT.

It's not a one and done type treatment.
After the SLAM, FC will drop as a percentage of total FC. A higher CYA will slow down that process.
It is save to swim in the pool with FC anywhere between minimum and SLAM level as indicated on the
FC/CYA Levels and you can see the bottom of the pool throughout its entire length.

Keep your FC on the high side of the target range for your CYA.

 

[Newdude]

Algae is not inviting for me to swim at all

Algae is harmless, but the canary in the coal mine. If it can flourish, so can the nasties that you can't see like bacteria and viruses. A little algae growing in a corner somewhere will never hurt you but it certainly points to a much larger issue that needs addressing asap.

(I know you know Ben. I quoted you for OPs benefit)

 

[mgtfp]

Got it. Follow up question then

If I raise the FC to 28ppm (SLAM level when CYA is 70), how many days before FC goes back to 5? Right now I'm losing about 1ppm per 24h. So will it take 23 days, or is the FC daily loss higher when its concentration is higher?

Chlorine loss is proportional to the chlorine level. Especially while there is algae, that's actually why we elevate FC for a SLAM, even though it may seem like a paradox at first. Higher FC means that the rate that chlorine is killing algae with is faster. As a kind of side effect you then of course also lose chlorine faster. Hence the "M"in SLAM, you need to maintain high FC so chlorine can quickly kill algae.

Chlorine loss to UV is also faster at higher FC, that's why we don't always maintain SLAM-level (but you can safely swim at SLAM-FC, nothing wrong with that), you would just waste unnecessary amounts of chlorine to UV. The recommended SLAM-levels have been chosen as a compromise between fast enough algae killing rates, but still manageable losses to UV (in the sense that during a SLAM your main chlorine-loss source is algae, not UV), and safe chlorine levels for swimmers and equipment.

The root of your question seems to be that you are worried about how long it takes for FC to come back down to "normal" levels once the SLAM is finished.

The answer is: Don't worry about that. As I have said, SLAM-FC (according to your CYA-level) is safe to swim in and not harmful to your pool. As long as you can see the bottom of the pool (everywhere, including deep end, of course), you can swim in any FC between min-Level and SLAM-level.

The only downside to maintaining SLAM-FC during normal operation is that you have unnecessarily high FC-loss to UV. But there is nothing wrong with for example an SWG sometimes overshooting a bit, even up to SLAM-FC. Better a bit too much FC than too little - that costs you in the long run a lot more chlorine, because algae creeps in eventually (as you have noticed), creating extra chlorine demand and making a SLAM necessary.

 

[kellyfair]

Do you have a SWCG?

 

[JJ_Tex]

If I raise the FC to 28ppm (SLAM level when CYA is 70), how many days before FC goes back to 5?

This is your problem. Assuming no SWCG, 5 is the bare minimum and the target should be 8-10. Get panicked if it drops below 8 (see my avatar on how high I like my chlorine).
Even if you do have a SWCG, if you are getting algae at 5, bump up your chlorine to 8 as 5 isn't working for you.

 

[kellyfair]

I would even turn SWCG off during a SLAM. Save those generating hours for normal use, and use liquid chlorine to SLAM.

 

[Pierrot]

The root of your question seems to be that you are worried about how long it takes for FC to come back down to "normal" levels once the SLAM is finished.

The answer is: Don't worry about that. As I have said, SLAM-FC (according to your CYA-level) is safe to swim in and not harmful to your pool. As long as you can see the bottom of the pool (everywhere, including deep end, of course), you can swim in any FC between min-Level and SLAM-level.

As much as I value TFP community, I still have a hard time believing that 28ppm of chlorine is safe, given that the max concentration allowed in California is 10ppm in public pools. So maybe it's unnecessary, but when it comes to the safety of my family, I prefer erroring on the side of caution. So nobody at home will swim until it's back under 10
Thanks for the explanation of the FC consumption depending on the FC concentration, very helpful.

This is your problem. Assuming no SWCG, 5 is the bare minimum and the target should be 8-10. Get panicked if it drops below 8 (see my avatar on how high I like my chlorine).
Even if you do have a SWCG, if you are getting algae at 5, bump up your chlorine to 8 as 5 isn't working for you.

Yeah when I say I have 5ppm, that's the min. Basically, I measure my FC at the end of the day, it's usually 5ppm, then I add liquid chlorine. So I assume I'm always between 5 and 6 or 7.

Do you have a SWCG?

Nope. I'm adding a bit of liquid chlorine every night.

 

[Bperry]

As much as I value TFP community, I still have a hard time believing that 28ppm of chlorine is safe, given that the max concentration allowed in California is 10ppm in public pools. So maybe it's unnecessary, but when it comes to the safety of my family, I prefer erroring on the side of caution. So nobody at home will swim until it's back under 10

Be careful following that. They allow up to 10ppm with zero CYA and Thats crazy harsh. Make sure you have at least 20-30ppm CYA if you plan to swim when the FC is 10ppm.

 

[mgtfp]

As much as I value TFP community, I still have a hard time believing that 28ppm of chlorine is safe, given that the max concentration allowed in California is 10ppm in public pools. So maybe it's unnecessary, but when it comes to the safety of my family, I prefer erroring on the side of caution. So nobody at home will swim until it's back under 10
Thanks for the explanation of the FC consumption depending on the FC concentration, very helpful.

They allow 10ppm without CYA, where I wouldn't put a toe in.

These rules are in absolutely no correlation with science.

TFP's SLAM-FC (e.g. FC 12 for CYA 30, or FC 24 for CYA 60) is equivalent to FC 0.64 without CYA. Make up your own mind what that means for FC 10 without CYA.

The core of the issue is that people don't understand the chemistry of chlorinated cyanurates.

Without CYA, there are two chlorine species showing up in the FC test. Hypochlorous acid (HOCl) and hypochlorite ion (OCl^-). At low pH, mainly HOCl, at pH 7.5 both at about 50%, at high pH mainly OCl^-. HOCl is the powerful sanitizer and oxidizer that we are interested in, which is why without CYA one should target a pH below 7.6.

Regulations for public pools (operated without CYA) in Europe consider this, and limit FC (in normal pool operation) to 0.6 (at pH 7.5 equivalent to HOCl 0.3).

When adding CYA, more than 95% of the chlorine is now attached to CYA, where it is protected from UV light, but has no sanitizing and oxidizing powers anymore. None at all. But unfortunately it still shows up as FC in the test.

That's why you need to adjust FC to the CYA level, so that the remaining 5% of "real free" or "active" chlorine provide sufficient amounts of HOCl. The HOCl concentration is proportional to the FC/CYA ratio. In other words, FC 12 / CYA 30 and FC 24 / CYA 60 provide same amounts of HOCl, which is the same amount that FC 0.64 with CYA 0 provides.

The chlorinated cyanurates provide basically a chlorine reservoir. As soon as HOCl and OCl^- get used up by UV or killing "stuff", more gets released from the reservoir until a new equilibrium between all the species is established (which happens pretty much instantaneously).

The reservoir also has an effect on the pH dependency of the HOCl concentration, with rising pH more HOCl gets released from the "reservoir", compensating to a large degree the change of HOCl into OCl^- with rising pH.

Without CYA, the HOCl concentration decreases by 50% between pH 7.5 and 8.0. With CYA this is only 15%, allowing pool operation at higher pH where pH-rise due to CO2 outgassing is much less of a problem.

CYA basically enables operating residential outdoor pools without fancy real-time test and dose equipment that would be required to maintain FC between 0.2 and 0.6.

But it requires acknowledging that FC needs to get adjusted to CYA, to ensure sufficient, but also not too little amounts of HOCl.

Legislations that allow FC between 1 and 10ppm independent from CYA levels exist solely because politicians got lobbied by the pool industry to implement regulations that work in their favour, ensuring maximum profitability.

They allow on one hand FC 1 or 2 with CYA 100, which will lead quickly to an algae bloom, resulting eventually in no FC holding at all.

And on the other hand they allow FC 10 with CYA 0, which makes you smell like a bleach bottle and wrecks your swimming gear in no-time.

But they close a pool that sits at FC 12 with CYA 30. This doesn't make sense at all, it just reflects the ignorance of politicians and bureaucrats.

Up to you...

 

[Pierrot]

In other words, FC 12 / CYA 30 and FC 24 / CYA 60 provide same amounts of HOCl, which is the same amount that FC 0.64 with CYA 0 provides.

Great post, love it, lots of insights thank you.

I'm convinced that FC 12 / CYA 30 and FC 24 / CYA 60 are equivalent in terms of sanitizing power. But to me, this doesn't necessarily translate into "FC 12 / CYA 30 and FC 24 / CYA 60 are equivalent in terms of dangerousness for humans".

Are there any studies showing that if a kid ingests a FC 24 / CYA 60 water it will have the same effect as FC 0.64 / CYA 0? I assume that the chemical reactions happening inside a body are different from what happens in a pool.

 

[Bperry]

Great post, love it, lots of insights thank you.

I'm convinced that FC 12 / CYA 30 and FC 24 / CYA 60 are equivalent in terms of sanitizing power. But to me, this doesn't necessarily translate into "FC 12 / CYA 30 and FC 24 / CYA 60 are equivalent in terms of dangerousness for humans".

Are there any studies showing that if a kid ingests a FC 24 / CYA 60 water it will have the same effect as FC 0.64 / CYA 0? I assume that the chemical reactions happening inside a body are different from what happens in a pool.

I wouldn’t drink water that had any CYA in it. I dont think anyone is arguing that its safe to drink, just swim in.

 

[mgtfp]

In the end it comes down to teaching kids to not drink pool water.

In regards to CYA, Trichlor and Dichlor are approved chlorinating methods for drinking water, but we are talking here about adding a few ppm of CYA, not 50 or 80, of course. Dichlor is also used in water purification tablets for hiking.

There are a few publications from David Wahman from the EPA on this topic (using chlorinated cyanurates, not about safe chlorine levels), mainly about calculating HOCl concentrations in the presence of CYA. Basically what John Wojtowicz and later Richard Falk (chem geek) have done in regards to pool water chemistry, going back to the original work from O'Brien.

In this post, Richard was linking to an EPA publication and putting the numbers into a pool context:

The FC level itself becomes relevant if you were to drink a lot of pool water. The EPA limit is 4 ppm FC for drinking water assuming consumption of 2 quarts per day for a lifetime. So 28 ppm FC is 7 times this limit so if you drank 4.6 fluid ounces (somewhat more than half a cup) of pool water you'd be at your daily limit according to the EPA drinking water standards (see this link), but according to the EPA in this link, the No Observed Adverse Effect Level (NOAEL) for long-term consumption is 14.4 mg/kg/day in rats but with the factor of 100 margin of exposure this gets down to 0.1 mg/kg/day. For a 20 kg (44 pound) child, this would require drinking 0.07 liters (2.4 fluid ounces) per day of 28 ppm FC water.

Unfortunately, the link is dead by now because the EPA has moved from ancient html to more modern webpages, but it is still accessible via Wayback:

U.S. EPA IRIS Substance file - Chlorine; CASRN 7782-50-5

Or here the current document in PDF form:

https://iris.epa.gov/static/pdfs/0405_summary.pdf

I see it like that: Reaction rates are determined by the actual oxidizer concentrations. You are happy to let your kids drink from the tap, containing up to 4ppm FC.

A slammed pool has maybe 0.6ppm of FC, so roughly 6 times slower reaction rates. But of course a higher total amount of chlorine with the CYA reservoir gradually releasing all of the chlorine, but also with gradually sinking oxidizer levels (by the time the chlorine reservoir has been halved, active chlorine levels have also halved).

This means that a pool with CYA 60 that's at FC 24 SLAM-level has 6 times lower active chlorine levels and accordingly slower chemical reaction rates, but 6 times more chlorine in total available. This means that an accidental gulp of pool water of let's say 50ml is in terms of total chlorine amount (I don't mean TC here with total) equivalent to 300ml of tap water containing FC 4 without CYA.

I am happy for my son to drink a glass of tap water, I even encourage him to so from time to time (I personally prefer to drink it filtered, but my son is usually to impatient to wait for a glass to fill from the tap with the filtered water). Consequently, I don't freak out when he occasionally swallows a bit of pool water. Chlorine is probably the smallest concern then.