Should CC go up when doing a SLAM?

[PoolGirlPlease!]

Hello! This is my first post here ever! So.... My out-of-ground 15,000 gallon pool has been greenish and cloudy for two weeks. TWO /HOT/ WEEKS! I used a bunch of pool store on the pool to no avail. So, I found this place (thankfully). Here's where I am right now:

I flocked the pool (before reading your advice) and I've vacuumed a ton of Crud to waste.
Yesterday, I brushed down the entire floor and walls (which were definitely algae-coated)
Yesterday, I changed the sand in my filter (I went to just clean it, but the tube thingy got stuck to the top and pulled out, so I decided to start fresh).
I purchased the recommended Taylor Pool Kit (but not "C" because too costly) and tested yesterday. FC 0.8 ppm. CC 0.6 ppm.
I lowered Ph to desired range.
I can't figure out pool calculator, so I just added two gallons of super shock yesterday last night and tested this morning: FC 8.4 ppm; CC 1 ppm.
I added another gallon of super shock and waited two hours to test: FC 14.2 ppm. CC 0.6 ppm.
The water looks clear.

QUESTIONS:
How much more shock should I add now to get it to 16-20 range?
How many more gallons (about) of liquid chlorine should I have on hand?
Is it possible that the CC level went up overnight, or did I just mis-test this morning?
Is my CC really bad or just a little? I'm wondering how many days of this SLAM until I can swim (preferable before September)?!

Thank you!

 

[PoolGirlPlease!]

And..... How do I know how much liquid chlorine to add each day to get to and maintain desired level?

 

[Bperry]

Welcome. If you have downloaded poolmath app on your phone, it’ll tell you how much liquid chlorine to add to reach the target. Just estimating that if you added 1 gallon of chlorine and it raised your FC level by ~6ppm, you can use that as an estimate on how much more you need to add. If you need to raise it by 4ppm, then add about 2/3 gallon.

You can swim in the pool right now, there’s no reason not to as long as the FC level is at or below the SLAM level for your CYA measurement and you can see the bottom of the pool.

CC of 0.5ppm or less is totally normal and considered “zero”.

 

[DrewLG]

How much more shock should I add now to get it to 16-20 range?

From your posted measurements, one gallon should do it.

How many more gallons (about) of liquid chlorine should I have on hand?

At first, you'll probably be using around two and a half gallons a day to get rid of the algae. That will diminish as the algae dies. Once the algae is gone and you're just maintaining your FC level, it'll be more like one or two quarts per day.

If you want to minimize trips to the store, buy 20 gallons of liquid chlorine now.

Is it possible that the CC level went up overnight, or did I just mis-test this morning?

Could be either one.

Is my CC really bad or just a little?

Not bad at all. But the most important thing for you now is the overnight FC loss, which appears to be 4 to 8 ppm currently, indicating that algae is present. You can't stop the SLAM until that overnight loss is at 1ppm or less, so you don't even need to bother measuring CC until the overnight loss drops to that level.

I'm wondering how many days of this SLAM until I can swim (preferable before September)?!

If you can see the floor of the pool, you can swim now.

 

[PoolGirlPlease!]

Thank you so... much, Bperry! My phone can't handle another app, but I tried it on the computer and had difficulty. Thank you for the estimate! I am trying to get to the SLAM level of 16-20 based on my CYA of around 45.

I thought that an FC level of 16 is too high to swim in. I found the following at Low Free Chlorine: How To Raise Free Chlorine Levels | Pool Marvel.
"Generally, the ideal range for free chlorine in pool water is 1-3ppm, although it depends on your cyanuric acid level and how much you swim. When the cyanuric level (CYA) is 30, the minimum free chlorine is 2. When it’s 40, the minimum free chlorine is 3. For cyanuric levels of 50, the minimum free chlorine is 4. A cyanuric acid level of 60 should have a free chlorine level of 5."

My CYA is between 40-50, so I think my FC should be between 3-4. I had read you should only swim if FC is 4 or less..... Can you shed any light on that?

Regarding CC, mine is above .5ppm. It's .6 ppm. I think that I am supposed to maintain the SLAM level of FC (16-20 ppm for my CYA level of 40-50) until my CC is .5 or less, but now it's .6 ppm.

QUESTION:
So, are you saying that you think it's ok to swim with such a high chlorine level, or, are you saying that maybe I don't need to continue to SLAM my pool and can just let the FC number drift back to 4-5, and then go in and enjoy the rest of what's left of the summer?

Thank you again, so much!

 

[PoolGirlPlease!]

From your posted measurements, one gallon should do it.


At first, you'll probably be using around two and a half gallons a day to get rid of the algae. That will diminish as the algae dies. Once the algae is gone and you're just maintaining your FC level, it'll be more like one or two quarts per day.

If you want to minimize trips to the store, buy 20 gallons of liquid chlorine now.


Could be either one.


Not bad at all. But the most important thing for you now is the overnight FC loss, which appears to be 4 to 8 ppm currently, indicating that algae is present. You can't stop the SLAM until that overnight loss is at 1ppm or less, so you don't even need to bother measuring CC until the overnight loss drops to that level.


If you can see the floor of the pool, you can swim now.

Even with an FC level of 16 ppm in the pool? I thought that over 4 ppm it wasn't such a good idea. Could you advise? Thank you!

 

[BoringDamo]

I’d suggest starting by reading some of the pool school articles. The method we preach here is perhaps a bit different than on other sites but is based on science and 1000s of pool owners who know it works. The industry is slowly catching up but very very slowly so most places will teach you things that just don’t work.
The core to TFP is do your own testing and know what effects the things you put in your pool will have. On a day to day basis this will likely only be liquid chlorine (doesn’t add any unwanted extras like the tabs or granules do) and muriatic acid to control ph.
The FC / CYA relationship table is key. You should never let you FC get below the minimum and most of us target a touch above the target level (it gives us a bit of breathing space).
For a SLAM the FC requirements are higher but are still based on your CYA level ( there is no in between, always round up so your CYA is 50). *** It is safe to swim in water with FC levels up to your SLAM level *** (ignore the max 4ppm rubbish advice) as long as you can see the bottom of the pool at its deepest part.
Happy Slamming!! I’d wish you luck but you don’t need luck. It just works if you follow it correctly. If you have questions keep posting back here.

 

[Bperry]

Thank you so... much, Bperry! My phone can't handle another app, but I tried it on the computer and had difficulty. Thank you for the estimate! I am trying to get to the SLAM level of 16-20 based on my CYA of around 45.

I thought that an FC level of 16 is too high to swim in. I found the following at Low Free Chlorine: How To Raise Free Chlorine Levels | Pool Marvel.
"Generally, the ideal range for free chlorine in pool water is 1-3ppm, although it depends on your cyanuric acid level and how much you swim. When the cyanuric level (CYA) is 30, the minimum free chlorine is 2. When it’s 40, the minimum free chlorine is 3. For cyanuric levels of 50, the minimum free chlorine is 4. A cyanuric acid level of 60 should have a free chlorine level of 5."

My CYA is between 40-50, so I think my FC should be between 3-4. I had read you should only swim if FC is 4 or less..... Can you shed any light on that?

Regarding CC, mine is above .5ppm. It's .6 ppm. I think that I am supposed to maintain the SLAM level of FC (16-20 ppm for my CYA level of 40-50) until my CC is .5 or less, but now it's .6 ppm.

QUESTION:
So, are you saying that you think it's ok to swim with such a high chlorine level, or, are you saying that maybe I don't need to continue to SLAM my pool and can just let the FC number drift back to 4-5, and then go in and enjoy the rest of what's left of the summer?

Thank you again, so much!

There are all kinds of website saying different things about chlorine and pool care. This website is dedicated to one specific method of pool care called TFP. All of the recommendations are explained with documented reasoning. Some people say this is the “science” based way (science doesn’t really say anything, scientists do and anyone can call themselves a scientist).

It’ll help if you read through the pool school articles on this website and learn about it. It’s really pretty simple. Here’s the big picture stuff:
1. Don’t put anything in the water that you don’t know exactly what it will do.
2. Don’t trust any water test results that you don’t do yourself.
3. Safe chlorine levels are always dependent on the CYA level. The higher the CYA level, the more chlorine is needed to maintain sanitary water. So it’s not possible to make blanket statements that say 5ppm (or whatever) is unsafe to swim in.

You can safely swim in the water if the chlorine level is below the SLAM level shown on the chart. My pool was at 10ppm last week and we went swimming, but only because I have enough CYA in the water to balance it.

 

[BoringDamo]

And the other good thing is we all preach the same advice.
Snap @Bperry.

 

[Bperry]

Thank you so... much, Bperry! My phone can't handle another app, but I tried it on the computer and had difficulty. Thank you for the estimate! I am trying to get to the SLAM level of 16-20 based on my CYA of around 45.

I thought that an FC level of 16 is too high to swim in. I found the following at Low Free Chlorine: How To Raise Free Chlorine Levels | Pool Marvel.
"Generally, the ideal range for free chlorine in pool water is 1-3ppm, although it depends on your cyanuric acid level and how much you swim. When the cyanuric level (CYA) is 30, the minimum free chlorine is 2. When it’s 40, the minimum free chlorine is 3. For cyanuric levels of 50, the minimum free chlorine is 4. A cyanuric acid level of 60 should have a free chlorine level of 5."

My CYA is between 40-50, so I think my FC should be between 3-4. I had read you should only swim if FC is 4 or less..... Can you shed any light on that?

Regarding CC, mine is above .5ppm. It's .6 ppm. I think that I am supposed to maintain the SLAM level of FC (16-20 ppm for my CYA level of 40-50) until my CC is .5 or less, but now it's .6 ppm.

QUESTION:
So, are you saying that you think it's ok to swim with such a high chlorine level, or, are you saying that maybe I don't need to continue to SLAM my pool and can just let the FC number drift back to 4-5, and then go in and enjoy the rest of what's left of the summer?

Thank you again, so much!

Forgot to reply that yes you need to keep slamming the pool and you can also continue to swim in it. If it’s got green algae then it’s because the algae is alive and growing. The only reason you stop a SLAM is when all three of these are true:
1. The water is crystal clear with no sign of cloudiness or algae on the pool surfaves
2. You pass an overnight chlorine loss test
3. You have a CC measurement of 0.5ppm or less.

You can keep swimming until all of those are done as long as you can see a drowning swimmer under water.

 

[DrewLG]

Even with an FC level of 16 ppm in the pool? I thought that over 4 ppm it wasn't such a good idea. Could you advise? Thank you!

Yes, even with 16ppm FC in the pool. It's ok because you also have CYA in the water, so your pool has less of the damaging and irritating (and disinfecting) hypochlorous acid than a pool with 4 ppm FC and no CYA.

If you feel like reading for a bit, the graphs below will explain why. Note that this information is also in the Pool School articles that discuss the FC/CYA relationship; the graphs I'm using are from an article referenced there.

Ok, this graph shows how chlorine works in a pool without any CYA:



What the graph shows is that when you add chlorine to pool water without CYA, the chlorine combines with the water to form two compounds: hypochlorous acid (the red line, HOCl, which is what kills algae and bacteria, and is also what irritates skin) and hypochlorite ions (the green line, OCl-, which doesn't really do much of anything). The amount of each is dependent on the water's pH; the mixture ranges from nearly 100% HOCl at a pH of 6.0, to a 50-50 mix at a pH of 7.5, to nearly 100% OCl- at a pH of 9.0.

Some important facts:

• The test for "free chlorine" (FC) doesn't just measure the concentration of the active, disinfecting HOCl; it lumps HOCl and OCl- together and measures the concentration of that combination.
• HOCl and OCl- don't last very long in the presence of UV light. On a sunny day, 90% of it could be gone in an afternoon.
• Very little HOCl is necessary to keep water sanitized. Even 0.05 ppm -- half a teaspoon in a 10,000 gallon pool -- is enough, and 0.1 ppm is plenty.
• If the pH stays constant, the ratio between HOCl and OCl- also stays constant -- the two are in equilibrium. So if some HOCl is used up (by oxidizing in the presence of UV, or by doing its job and combining with organic contamination to produce chloramines), some of the OCl- will become HOCl in order to keep the ratio constant.

So that's why you hear recommendations for only around 1 or 2 ppm of free chlorine and a pH of 7.2 to 7.6: In a pool without CYA, with pH between 7.2 and 7.6, 1 ppm FC makes available between 0.4 ppm and 0.6 ppm of HOCl, which is enough to keep the pool sanitized all day even if most of the chlorine is burned off by the sun.

For a little protection from testing error, or to reduce the necessary frequency of chlorine maintenance, the CDC and pool manufacturers say that up to 4 ppm free chlorine is allowable. But they don't allow more than that, because in a pool without CYA, 4ppm FC could mean over 3 ppm of HOCl if the pH is high, and that's enough to really irritate skin and even damage equipment over enough time.

That's also why even the most basic pool testing kit includes a pH test: In a pool without CYA, pH can adjust the amount of HOCl from around 5% to around 95% of free chlorine. And since we can't measure the concentration of HOCl directly -- we can only measure free chlorine, which is the combined concentration of HOCl and OCl- -- we need to know the pH in order to determine whether there's enough HOCl to sanitize the water.

Ok, now a pool with CYA, like yours:

This graph shows what happens when you add 3 ppm chlorine to pool water that contains 30 ppm CYA. It forms some HOCl (red line) and some OCl- (green line), as before, but this time the overwhelming majority of the chlorine is "stabilized" by weakly attaching to CYA molecules. This stabilized chlorine (blue line) doesn't do anything to sanitize your pool; it's just held "in reserve", protected somewhat from the sun by the CYA.



In the normal range of swimming-pool pH, 7.0 to 8.0, the ratio among the compounds is approximately 95% stabilized chlorine, 5% the other two. As before, the "free chlorine" test measures the concentration of all the chlorine compounds combined. And also as before, the chlorine compounds -- HOCl, OCl-, and stabilized chlorine -- are in equilibrium. So if some HOCl gets used up, some of the stabilized chlorine is released and becomes HOCl to replace what was lost (and a tiny bit of the OCl- becomes HOCl, too).

But the most important thing to notice here is that even with 3 ppm FC, a pool with 30 ppm CYA will only contain around 2.5% of the FC as HOCl. Compare that to the pool in the no-CYA graph, which has 50% of its FC as HOCl.

Doing the math, the pool with 3 ppm FC and 30 ppm CYA has 0.075 ppm HOCl -- still enough to keep the pool sanitized and algae-free, but only around 1/10 as much as in a pool with 1ppm FC and no CYA.

 

[kimkats]

Following along and jumping in to say: Well done all! From the OP to the ones that are helping them!!!

 

[PoolGirlPlease!]

This has all been super helpful! I am looking forward to the results from my first overnight test tomorrow morning. I love testing too! I feel like a mad scientist.