Need some basic advice -TA, pH, CH, FC all things chemical

[IceShadow]

Also part of the issue a lot of people doing a SLAM have is hidden algae. You have to find those spots where algae is hiding and scrub them out. A one-time dump won’t give you much time to find everywhere it could be hiding.

 

[IceShadow]

Here’s my old original liner color vs. what the pool had.

 

[mgtfp]

That post might be helpful:

How much chlorine is too much?

I am trying to find data on how much chlorine is too much or unhealthy. That is, at what point do the harmful effects of chlorine out weigh the benefits of the chlorine's ability to disinfect? I am a regulator for a local health department, and as such I do not have a single pool that I care...

www.troublefreepool.com

 

[JoyfulNoise]

Well, for one, it’s a massive waste of chlorine. The assumption in your conjecture is that the high levels of chlorine are all going towards disinfection or oxidation but in reality that’s not true. Some of it just burns off (gets reduced) by sunlight or breaks down on it own and those reactions are concentration driven. The higher the concentration, the faster they proceed. Chlorine isn’t cheap.

And yes, equipment is not designed to handle large amounts of chlorine like that. Pump and valve seals will all be exposed to chlorine causing oxidation damage. Any internal metallic components will see enhanced levels of corrosion. Copper heat exchangers can be stressed.

Most plaster pigments, especially blue ones, are not inorganic. Some are, but a lot are not. So chlorine does bleach plaster surfaces. I had a plaster crack patched in my attached spa once and when they chipped out the area you can clearly see how gray the “Caribbean Blue” surface layer was for several millimeters and then the bulk of the plaster was the original blue color. That’s all from chlorine exposure.

Now your idea of high chlorine is not without merit. In fact, pool guys in the industry will often resort to it when they come up against a swamp pool. I call it the “shock & floc” method - they will lower the pH to 6.8, add about 100ppm to 150ppm of chlorine (and sometimes a cheap algaecide) and then wait 24 hours with filtering ( someone gets left to watch and backwash the filter, usually the pool owner). They come back the next day and the pool has gone from solid green to the hazy grey. Then they add floc, recirculate for 30mins or so and then shut off the pump. Then they come back later that day and vacuum the pool to waste. The pool is clear (mostly but not TFP clear) and then they tell the owner to not swim until the chlorine comes down to normal. Does it work? Yeah. Does it potentially do lots of damage to pool surfaces and equipment? Yeah, but that rarely shows up right away and just gives the pool service guy more business.

TFP’s SLAM method is based on not only what works, but also what is easiest for the average pool owner to accomplish. It takes a long time but it also teaches valuable lessons at the same time - the pool owner begins to understand how water chemistry is managed and what it take to keep a pool clean and clear. The last thing TFP ever wants to teach anyone is how to get away with shortcuts and rely on tricks or gimmicks to make a pool do what you want. That’s what the industry pushes and the reason why so many people wind up here in absolute frustration.

As is always said - it’s your pool and your time (and money) so you can do whatever you like…

 

[Rancho Cost-a-Lotta]

Well, for one, it’s a massive waste of chlorine. The assumption in your conjecture is that the high levels of chlorine are all going towards disinfection or oxidation but in reality that’s not true. Some of it just burns off (gets reduced) by sunlight or breaks down on it own and those reactions are concentration driven. The higher the concentration, the faster they proceed. Chlorine isn’t cheap.

I saw the accelerated degradation of chlorine at high FC levels as I completed a SLAM for mustard algae. Regular SLAM level for my CYA is 31. MA SLAM is 44 ppm. During the first 24 hour period coming off the SLAM, FC dropped from 44 to 28 (- 16 ppm). Next day, FC dropped from 28 to 21 (-7 ppm), then 21 to 15 (-6) the following day. As FC neared recommended CYA levels, daily loss dropped to 2.5 ppm.

 

[SoDel]

I think I found something. Pool chlorination and closure guidelines | National Collaborating Centre for Environmental Health | NCCEH - CCSNE

Unfortunately the Erdinger article it refers to is in German and seems to focus much more on disinfection byproducts than FC, but anyway the linked article gives some support for a 5 ppm FC limit (due to possible ingestion, although it also mentions short term ingestion up to 50 ppm showed no ill effects) and a 10 ppm FC limit (due to eye and mucosa irritation).

 

[SoDel]

I saw the accelerated degradation of chlorine at high FC levels as I completed a SLAM for mustard algae. Regular SLAM level for my CYA is 31. MA SLAM is 44 ppm. During the first 24 hour period coming off the SLAM, FC dropped from 44 to 28 (- 16 ppm). Next day, FC dropped from 28 to 21 (-7 ppm), then 21 to 15 (-6) the following day. As FC neared recommended CYA levels, daily loss dropped to 2.5 ppm.

This is the sort of thing I have in mind (but perhaps I’m taking it to an extreme). Raise the FC extremely high (at night) and it will remain in the elevated range for a relatively short period of time (days) but plenty of contact time to kill and oxidize the nasties.

Anyway, I see many good reasons have been given not to actually do this In a pool.

 

[proavia]

You are taking it to an extreme amd way over thinking it.
Much easier to learn and follow TFP recommendation and prove to yourself that it really works.

There are years and years of experience in the forum amd articles TFP offers. If the TFP method didn't work, this place would have died off a long time ago.

 

[PowerPigg!!]

This may not be strict scientific method, but I actually performed the experiment as a result of a, shall we say, spirited marital disagreement about the wisdom of slamming vs our old Pool Guy's quick bottle pour approach. Last year had a lot of challenges and one of the things that got set aside for my sanity was care of the pool during the winter months.

This led to a tiny swamp that needed to be tamed, but we disagreed on how quickly it must get done. I provided a timetable of about 4 days informed by cost, practicality, and this universe's laws of physics; she wanted 1 day. She also suggested that she called Pool Guy for his expert guidance and he said he could do it no problem.

Sensing a learning moment forming, I immediately recognized the error of my ways, my foolish adherence to evidence-based pool control, and gleefully allowed myself to be led to the slaughterhouse.

The very first thing to be done was, of course, to dump a full 2.5 gallon jug of 12% chlorine into the pool over the same spot. No stirring of the water and no turning on of the pump until the next day--doctor's orders.

I died a little inside. But, as great men once willingly withstood torture and exile rather than renounce truth, so did I stand firm in the face of liner abuse. This was, after all, for Science. Mostly.

Pool Guy was allowed to perform additional wallet reduction exercises for two more days-- the amount of time it took for marital recognition that the 1 day deadline had come and gone. Pool Guy was then sent on his merry way.

Today Pool Guy is gone, but I will always remember him. I have a visual reminder of the fleeting moment he touched our lives--our pool's drunk tattoo.

 

[tim5055]

Here is the thread you will want to read. @chem geek did a lot of the early studies on the CYA/FC relationship.

He hasn't participated here in a couple of years, but we still have his original writing all over the forum.

Pool Water Chemistry

This thread presents my findings so far on pool water chemistry including the following: More Accurate Calcite Saturation Index (CSI) to replace Langelier Saturation Index (LSI) Calculation of ppm HOCl (disinfecting chlorine) at various levels of Total Free Chlorine (FC) and Cyanuric Acid (CYA)...

www.troublefreepool.com

 

[SoDel]

You are taking it to an extreme amd way over thinking it.
Much easier to learn and follow TFP recommendation and prove to yourself that it really works.

There are years and years of experience in the forum amd articles TFP offers. If the TFP method didn't work, this place would have died off a long time ago.

Yes, but I always need to know the “why” and to understand to the best of my ability exactly what I am actually doing. I do recognize that things generally are the way they are for a reason, but I have to understand the reason.

 

[proavia]

Yes, but I always need to know the “why” and to understand to the best of my ability exactly what I am actually doing. I do recognize that things generally are the way they are for a reason, but I have to understand the reason.

No time like the present to read thru all of the info here on TFP then. You will find all the answers to your questions (and alot more info).

I suggest you review all the Chemgeek articles first.

 

[JoyfulNoise]

Dosis sola facit venenum

Roughly translated - “it’s the dose that makes the poison…”

There are practical limits to everything one can do. The answer to your question is simply this - the downside risks of damaging your pool, or harming yourself, are not worth the marginal savings in the time you’d achieve. Is there something magical or amazing about a 40% Fc/CYA ratio during a SLAM? No. It was chosen as the target value to achieve workable results in a reasonable time frame with the least risks to persons or equipment. In other words, it’s the dose that achieves the cure without causing harm.

 

[mgtfp]

I think I found something. Pool chlorination and closure guidelines | National Collaborating Centre for Environmental Health | NCCEH - CCSNE

Unfortunately the Erdinger article it refers to is in German and seems to focus much more on disinfection byproducts than FC, but anyway the linked article gives some support for a 5 ppm FC limit (due to possible ingestion, although it also mentions short term ingestion up to 50 ppm showed no ill effects) and a 10 ppm FC limit (due to eye and mucosa irritation).

Well, take that article with caution, there are many of the "classical" mistakes in it.

To start with, they don't acknowledge the the FC/CYA relationship and treat FC as an independent parameter.

A few numbers to understand what this means:

Our SLAM level (FC = 40% of CYA) is equivalent to a HOCl-concentration ("active chlorine") of about 0.3-0.31 ppm. Without CYA, this is equivalent to FC of about 0.65ppm (at pH 7.5).

Our SWG-Target level (FC = 7.5% of CYA) is equivalent to a HOCl-concentration ("active chlorine") of about 0.03 ppm. Without CYA, this is equivalent to FC of about 0.07ppm (at pH 7.5).

10 ppm FC without CYA is equivalent to a HOCl-concentration of about 4.6ppm (at pH 7.5). This is equivalent to FC=55ppm at CYA=50ppm, or FC=83ppm at CYA=80ppm or roughly FC = 100-110% of CYA.

The point is, 10ppm FC without CYA is a lot. Equivalent to about 2.5 times more than TFP's SLAM-level. On he other hand, 10ppm FC at CYA=80ppm is equivalent to about FC=0.12ppm with no CYA.

Defining an FC-limit without a correlation to CYA is absolutely meaningless. It's like saying water boils at 100°C (212°F). This number is meaningless without referring to the air pressure. On Mt Everest, where air pressure is much lower, water boils at about 68°C (154°F) - you better consider that in your cooking time for pasta.

The other major mistake they are repeating in this article, is the wrong application of the "10 times" rule for breakpoint chlorination. The correct rule is that you need about 10ppm FC (measured in units of ppm Cl₂ to get rid of 1ppm ammonia (measured in ppm N). It is wrong to state that you need 10ppm FC for each 1ppm of CC. More about that for example here:

Is the formula for "Superchlorination" or "Shock" too high?

Is anyone trying the new formula for shocking (breakpoint chlorination) that Taylor and DuPont are suggesting in this article? Seems that the latest (2009) research suggests that the formula we've been using to determine the shock level of FC is really too high and itself contributes to the...

www.troublefreepool.com

 

[SoDel]

Well, take that article with caution, there are many of the "classical" mistakes in it.

To start with, they don't acknowledge the the FC/CYA relationship and treat FC as an independent parameter.

A few numbers to understand what this means:

Our SLAM level (FC = 40% of CYA) is equivalent to a HOCl-concentration ("active chlorine") of about 0.3-0.31 ppm. Without CYA, this is equivalent to FC of about 0.65ppm (at pH 7.5).

Our SWG-Target level (FC = 7.5% of CYA) is equivalent to a HOCl-concentration ("active chlorine") of about 0.03 ppm. Without CYA, this is equivalent to FC of about 0.07ppm (at pH 7.5).

10 ppm FC without CYA is equivalent to a HOCl-concentration of about 4.6ppm (at pH 7.5). This is equivalent to FC=55ppm at CYA=50ppm, or FC=83ppm at CYA=80ppm or roughly FC = 100-110% of CYA.

The point is, 10ppm FC without CYA is a lot. Equivalent to about 2.5 times more than TFP's SLAM-level. On he other hand, 10ppm FC at CYA=80ppm is equivalent to about FC=0.12ppm with no CYA.

Defining an FC-limit without a correlation to CYA is absolutely meaningless. It's like saying water boils at 100°C (212°F). This number is meaningless without referring to the air pressure. On Mt Everest, where air pressure is much lower, water boils at about 68°C (154°F) - you better consider that in your cooking time for pasta.

The other major mistake they are repeating in this article, is the wrong application of the "10 times" rule for breakpoint chlorination. The correct rule is that you need about 10ppm FC (measured in units of ppm Cl₂ to get rid of 1ppm ammonia (measured in ppm N). It is wrong to state that you need 10ppm FC for each 1ppm of CC. More about that for example here:

Is the formula for "Superchlorination" or "Shock" too high?

Is anyone trying the new formula for shocking (breakpoint chlorination) that Taylor and DuPont are suggesting in this article? Seems that the latest (2009) research suggests that the formula we've been using to determine the shock level of FC is really too high and itself contributes to the...

www.troublefreepool.com

See now what you’re saying is exactly what has been spinning around in my mind the past few minutes. On the one hand, the actual HOCL equivalence with the presence of CYA is a small fraction of the measured FC (and equivalent HOCL concentration without CYA). So on that hand, higher levels of FC with CYA still provide an extreme safety factor in terms of bather safety from chlorine. But on the other hand, very very high levels of FC also in the presence of CYA will (we are told) destroy vinyl, bleach plaster and corrode pool equipment. See what I mean — can this be squared somehow? (I omitted actual numbers so we can discuss the concepts — like the attenuation of HOCL equivalence provided by CYA either buffer the “evil” effects of high FC or they don’t — I think it has to but I need to think more on this.

[also I am interpreting the levels reprted in the article as assuming zero CYA — so 5 ppm is drinkable and less than 10 ppm is swimmable. As a “wiser” bunch, we can run the equivalents in the presence of CYA]

 

[IceShadow]

So on that hand, higher levels of FC with CYA still provide an extreme safety factor in terms of bather safety from chlorine. But on the other hand, very very high levels of FC also in the presence of CYA will (we are told) destroy vinyl, bleach plaster and corrode pool equipment. See what I mean — can this be squared somehow?

It’s a ratio. The more CYA you have, the more FC is buffered. If your CYA was 1000, FC 400 would be ok to swim in. (Maybe. Not gonna try anyhow.)

 

[SoDel]

It’s a ratio. The more CYA you have, the more FC is buffered. If your CYA was 1000, FC 400 would be ok to swim in. (Maybe. Not gonna try anyhow.)

Yes! Exactly! So where are we when CYA >= 30 (proportional result and I think “safe” HOCL equivalance even at “ridiculous” FC measurements).

For CYA at 1,000 and FC at 400, we need someone who can discuss chlorinated isocyanurates — will they kill us? Do they destroy pools? Calling all TFP’ers — how does all this actually work lol?

 

[mgtfp]

the actual HOCL equivalence with the presence of CYA is a small fraction of the measured FC (and equivalent HOCL concentration without CYA).

Just for completeness: Technically you also have to consider OCl^-, which also shows in the FC-test. OCl^- is not an efficient sanitizer, but still a powerful oxidizer. There is a chemical equilibrium between HOCl and OCl^-. At very low pH it's nearly all HOCl, at very high pH it's nearly all OCl^-. Somewhere between pH 7.4 and 7.5 it's 50/50. And with CYA, the vast majority of chlorine is bound to CYA, but still tests as FC.

can this be squared somehow?

In the end, it's about contact time, how long a certain chlorine level (or more precisely the HOCl level) is exposed to to bacteria/algae/pool equipment, as you have already pointed out in your first post.

And about manageability of FC levels. Just based on CT (product of chlorine and time), you could say that 10-times SLAM-FC for only a tenth of the time does the same to bacteria/algae/pool equipment than SLAM-FC for 10-times longer.

But as Matt already explained, such a high FC/CYA ratio is not manageable, you will lose much more to UV and thermal degradation than in killing algae. You had to basically constantly test and adjust FC, and end up needing huge amounts of chlorine. Draining to reduce CYA will usually be more efficient.

There is are other problems. If you for example killed all algae towards the evening and you keep up topping up chlorine until after sunset, ending up at FC levels that are even higher then your intended 10xSLAM. And then you're stuck with much of it over night and can quickly exceed your tenth of normal contact time, and do damage to a liner.

TFP's SLAM level is a good compromise between required times to clear a green pool, but on the other hand being well below CTs that would be dangerous to pool equipment. And with the typical bathing times also uncritical to bathers and their bathing suits.

Even at SLAM-FC (according to CYA-level), you can swim without noticing much of the chlorine or exposing your bathing suit to excessive wear. Whereas regular swimming at a public indoor with no CYA at FC of let's say 4ppm will result in bathing suits not lasting very long. There are some nice anecdotes from chem geek on that:

How much chlorine is too much?

I am trying to find data on how much chlorine is too much or unhealthy. That is, at what point do the harmful effects of chlorine out weigh the benefits of the chlorine's ability to disinfect? I am a regulator for a local health department, and as such I do not have a single pool that I care...

www.troublefreepool.com

 

[mgtfp]

CYA at 1,000 and FC at 400, we need someone who can discuss chlorinated isocyanurates — will they kill us? Do they destroy pools?

I don't think that's really relevant. We know from experience that CYA levels with their corresponding FC levels listed in the FC/CYA Levels are safe for bathers and pool equipment. If you exceed those CYA levels, a pool becomes unmanageable and needs draining.

 

[JoyfulNoise]

Can I just interject some actual experience into this thought-experiment … the vast majority of the time spent SLAM’ing a pool is in the clearing phase and really has nothing to do with sanitation or oxidation. When you add chlorine to a level of 40% of CYA, the algae is pretty much dead within a few hours and any bacteria that may have been in the water is completely wiped out. After the first 24 hours, the next 5 days is spent filtering the water. So even if you wanted to do some kind of super-shocking, it's not really doing anything useful. TFP suggests maintaining the SLAM level because, again, it's a good balance between keeping the water sanitary and the loss of chlorine. If one tried to maintain a level much higher than 40% of CYA, it would be nearly impossible to pass the exit criteria of less than 1ppm overnight chlorine loss simply because the thermal loss rate of chlorine would exceed that.