What is the algorithm used for daily chlorine doseage?

[rock]

Once a week or two, I can 'fix" bad water chemistry - but - I want to be more proactive daily.

Debugging a light algae coating, I just had my water read at Leslies:
FAC = 5 ppm (Leslies says this is high and should be 1 to 4 ppm so they want me to add 19 ounces by weight of Leslie's Chlorine Neutralizer)
TAC = 5 ppm
CH = 330 ppm
CYA = 50 ppm (I have three floaters, each with a handful of 3" Costco trichlor pucks)
TA = 130 ppm (Leslies says this is high and should be 80 to 120ppm so they suggest 62 ounces of muriatic acid)
pH = 7.6
TDS = 1,000 ppm
Pho = 500 ppb (Leslies says this is high and should be below 100 ppb)

According to the "Chlorine / CYA Chart", given 50 ppm CYA, my target FC should be 6 ppm.
According to the "Pool Calculator", I need 40 ounces of 12% by volume HASA liquid chlorine to raise the FC from 5 to 6 ppm (for a 38,500 gallon pool).

So, I just added 62 ounces of 28% muriatic acid (according to Leslie's calculation); and I added 40 ounces of HASA liquid chlorine (according to the two troublefree pool recommended tables above).
But, all this is corrective action ... just to get the pool chemistry to where it should have been all along.

Hence, my question (assuming the target of 6 ppm FC is the goal):
Q: How do I figure out what the daily (proactive) maintenance dose should be of liquid chlorine (given I have about five 3" trichlor tablets in each of three floaters, two for the pool and one for the spa)?
Note: A very sunny location (no shade whatsoever); water temperatures about 77°F to about 80°F; almost zero bather load (one swim per day for 5 minutes for one adult).

 

[jblizzle]

Easy.
First, you have to remove all the tablets because your CYA is already on the high end of the recommended range. (Or your CYA will keep building higher and higher and your FC will be too low and then you will have a green pool)

Then every day you use your Recommended Test Kit to determine your current FC level ... and make sure it is not below the minimum for your CYA.

Then you use the poolcalculator.com to determine how much bleach to add to get back up to the target level based on your measured FC level.

 

[rock]

remove all the tablets

Understood.
Up until a few weeks ago, CYA never was a problem, mainly because I had massive water leaks (500 gallons every couple of days) at the pumps (which are below grade by 8 feet) but now that I fixed the leaks, the CYA can only go up.

Then every day...determine your current FC level ... and make sure it is not below the minimum for your CYA.

Hmmm... I understand what you're saying. But I had *thought* there was a "daily maintenance dose" regimen that most people followed.
For example, that's kind of what I'm doing with the tablets (as I assume they dissolve relatively predictably.

So, may I confirm: Are you saying that there isn't really a proactive "daily maintenance dose" of chlorine; instead, you simply reactively correct it when it goes 1 point too low?

Then you use the calculator to determine how much bleach to add to get back up to the target level based on your measured FC level.

Do I really need the calculator once it told me today that to raise my FC from 5 ppm to 6 ppm, I needed 40 ounces of 12% (by volume) chlorine?

Doesn't that linear relationship (of 40 ounces to 1 ppm) hold true forever?
For example, if, say, tomorrow I needed to raise the FC by, say, 2 ppm, why would I again go to the Pool Calculator? Wouldn't I just add 80 ounces of liquid chlorine to raise the level by 2 ppm?

NOTE: The fact I'm asking these questions may indicate to you that I'm missing something fundamental - and maybe I am - hence my questions. Thanks.

 

[jblizzle]

It is a linear relationship.
What I laid out is the way to start ... by doing this, you will learn your pool and may be able to start to "predict" how much bleach you need to add everyday.

We always recommend you test to know where you are at and then dose to acheive your target.

Now we could make some speculations based on "normal" "clean" pools, but they may not be accurate for you. And you will not know this if you can not accurately test.
For example, losing 2-3ppm of FC every day is not unusual. So you may be needing to add 80-120oz of 12% everyday to raise the FC by 2-3 each day.

 

[woodyp]

You are correct: If 40 oz. equals FC by 1, then 80 oz. equals FC by 2.

 

[Richard320]

Let's go back to the basics.

1) You're letting the pool store test your water. With 200+ posts here, I'm really quite shocked at that. That free testing is worth every penny you paid for it. Check out the fluctuating readings given to this poster: inconsistency-in-readings-t61728.html

2) If you have algae, you need to SLAM it. Just adding a couple PPM bleach is not going to kill that algae

3) Stop using the pucks. They'll just keep raising CYA levels, which raises the minimum free chlorine level you need to maintain, which means more pucks, which raises the minimum free chlorine level you need to maintain, which means more pucks, ad infinitum. With 200+ posts here, I'm really quite shocked at that.

Q: How do I figure out what the daily (proactive) maintenance dose should be of liquid chlorine (given I have about five 3" trichlor tablets in each of three floaters, two for the pool and one for the spa)?
Note: A very sunny location (no shade whatsoever); water temperatures about 77°F to about 80°F; almost zero bather load (one swim per day for 5 minutes for one adult).

Test it every day until you get a feel for the chlorine consumption. How much will a teenage boy eat? You won't know until you see how much he eats, several days running. And you'll learn how much extra to cook after he's played a game of football. Once you know, it's not hard. Same with a pool. By watching the pool's appetite, you learn how much to feed it. Many of us get casual and just dump in the usual and test it every two or three days, but that's after long practice.

In your case, this is all hypothetical until you get rid of the algae

 

[techguy]

Three floaters with three pucks each are adding a ton of CYA each day. This was my method of maintaining my pool before fully understanding CYA and the BBB method. I thought the more pucks, the better. If I had green, I must need more pucks... stack a few more into the float. Problem is, whn you get your CYA to the 70-100 range (or higher) it's almost impossible (certainly impractical) to add enough chlorine to prevent the green.

Time to get a reliable test kit and SLAM that pool. I don't trust pool stores...

 

[rock]

you will learn your pool and may be able to start to "predict" how much bleach you need to add everyday.

That makes sense. The whole point of this thread was to figure out what algorithm is used. So, I thank you for explaining as it isn't what I had thought it was.

What I had thought was that there is a calculation for how much chlorine you need to proactively add to keep the level at a certain concentration permanently.
What you're saying is, in essence, that you test daily, and react daily (based on the pool chlorine demand), and, over time, if the chlorine demand is regular, this method of testing-and-reacting would probably end up being predictable.
But, what you're saying, it doesn't make as much sense to try to predict that chlorine demand ahead of time as it does to just daily control the pool chlorine level - and - the pattern of chlorine will emerge out of that.
OK. It's an algorithm that is logical and understood.

You are correct: If 40 oz. equals FC by 1, then 80 oz. equals FC by 2.

Thanks. For me, that makes things easy, as a gallon (128 ounces) of chlorine would be 3 ppm. What I've done today is marked out a large-mouthed orange-juice plastic jug in 40 ounce increments. Every time I need 1 ppm, I'll dose the pool with 40 ounces. The one problem is that my chlorine test kit (reading reddish colors) isn't really all that granular. I'd say I can read it to, oh, maybe plus or minus 2 or 3 ppm - so - it's not all that accurate for this method (I have the basic three bottle chlorine + pH kit).

You're letting the pool store test your water.

I test the chlorine & pH daily but that's it. I did have, in the past, the recommended test kit, but I could never get the same reading twice for some things, e.g., CYA. It seemed, to me, more subjective than it should have been. Plus, the pool store could test things for me and they have more practice in interpreting things, such as the CYA levels. However, they're dead wrong on their recommendations (e.g., on removing phosphates); so, I'll take their readings - but not their recommendations.

I do agree that they might not give the same reading twice, and, I should grab two or three bottles, and sequentially visit two or three stores, to prove whether their results actually do differ as much as the horror stories indicate.

If you have algae, you need to shock your pool.Just adding a couple PPM bleach is not going to kill that algae

Now *that* is interesting!

I thought the shocking was for oxidizing (burning up) organic stuff in the water, such as baby oils and suntan lotion, etc., not for living things. I thought merely having the right chlorine levels (plus brushing the pool to expose the algae to the chlorine) would kill that algae. Is that not the right assumption?

Can you confirm that merely having the right amount of chlorine to CYA ratio isn't enough to kill the existing algae?

Stop using the pucks. They'll just keep raising CYA levels

I pulled all three floaters out today.
I hadn't mentioned that I was losing about an inch of water, i.e., 500 gallons of water, every two days (solar heating and pool pump leaks), mostly when the system was shut off since both are well below grade. So, the CYA has never been a problem before. Plus, I have PLENTY of sunlight. So, a bit of CYA is a good thing. Yet, I do fully agree with you - and I've pulled the floaters. So now I'm only on liquid chlorine, as of today.

How much will a teenage boy eat?

That's actually a great example, as it gets the point across succinctly. I have to get a feel for the chlorine demand of my pool. There is practically zero bathing going on in the pool, so, most of the chlorine is going to be used up by the sun, and, I guess, the light dusting of green algae on the rough scratchy walls, until I get it under control.

Problem is, whn you get your CYA to the 70-100 range (or higher) it's almost impossible ... to add enough chlorine to prevent the green.

I just realized, while answering these questions, why my "old" system will no longer work.

Before I fixed the leaks, I was constantly adding water, so the CYA level wasn't a problem.
Paradoxically, the chlorine level, with the three floaters dissolving trichlor all the time, somehow maintained a relatively stable level of chlorine.
I'm not sure why the chlorine level didn't fluctuate down as much as the CYA did - but - the end result - it seems - was a relatively stable chlorine level.

Now that I've removed the pucks, the chlorine level will fluctuate more, as the liquid will be the SOLE source of chlorine.
Hence, the daily test-and-react method makes even more sense, under those circumstances.

I should make a regimen of testing late in the day, so that I can allow the chlorine added to work all night before the sun starts doing it away.

 

[jblizzle]

You should ...
Get and use a good test kit.
Apparently read Pool School a few more times as you are not grasping many things.
Go through the SLAM process.
Stop over thinking everything.

 

[chem geek]

The minimum FC level to target FC level relative to CYA only works when there isn't already established algae and when the circulation is reasonable so that the chlorine level doesn't get low locally. If there's already algae, then chlorine gets used up more quickly especially in the area of the algae and especially when the circulation in that area is poor. The SLAM process of elevating the chlorine to a high level as well as brushing the pool will kill the algae even if established and clumped.

Think of a wood pile (algae nutrients) getting sparks (algae spores) thrown at it. Think of chlorine as water mist or drops that puts out the sparks before they can start a fire (algae bloom). If the active chlorine level gets too low then the algae can grow faster than chlorine can kill it. If a fire starts, even a low level one, then normal active chlorine levels won't be enough, but an elevated chlorine level, a larger splash of water, can kill the algae (put out the fire).

However, without your own proper test kit there is no way to know what is going on since pool store testing has been shown to be incorrect quite frequently. Any conclusions you are drawing with their data cannot be considered to be valid. They might be true, they might not. Please get your own proper test kit, the TFTestkits TF-100 or the Taylor K-2006.

As for daily chlorine dosage, it varies by pool due to temperature, amount of sunlight, bather load, organics blown into the pool, and other factors. So there isn't a predictive algorithm and instead you determine the daily chlorine loss for your own pool. For most outdoor residential pool at the FC/CYA levels we recommend it's 2-3 ppm FC per day but some are lower (especially those with covers or under screens) and some are higher. As was noted, The Pool Calculator can calculate dosing if you put in the FC difference (between Now and Target).

 

[techguy]

To answer your question, there is an algorithm, its build into the poolcalculator.com and its all I need to know about the relationship.

 

[rock]

Go through the SLAM process.

OK. Well, there is a daily light dusting of algae on the deeper-end walls, so I need to follow your algorithmic suggestions, which, if I understand yet, is:
a. Richard's Chlorine / CYA Chart suggests a shock level of 20 ppm (based on CYA levels of 50 ppm)
b. The Pool Calculator says that every 40 ounces of HASA 12% by wt chlorine adds 1 ppm, so the pool will initially need just over about 4 gallons of liquid chlorine to add 128 ounces * 4 gallons / 40 ounces = 13 ppm to my existing 6 ppm.
c. The SLAM method suggests one of three test kits that I'll need to get.
d. I've put the filter pump on service override, and I'll manually brush the entire pool at least daily.
e. I'll perform the Overnight Chlorine Loss Test to see if the FC drops by more than 1 ppm overnight.
f. After I get the overnight chlorine loss to 1 ppm or less, I will remove and hose down the two filters to remove dead algae from the paper elements.
g. Then I will test daily, manually adding 40 ounces of HASA liquid for every 1 ppm needed to maintain a target FC level of 6 ppm.

If a fire starts, even a low level one, then normal active chlorine levels won't be enough

Thanks Richard. I now understand two of my three errors:
ERROR 1: I had not realized that the target chlorine level doesn't actually kill a light daily coating of algae.
ERROR 2: I'll need to forget my errant notion that shocking was mainly for high bather load and/or a green or turbid pool (my 6 ppm FC pool water is clear and the bathing load is near zero - but the pool grows a daily dusting of algae on the scratchy walls, mostly in the deep end and in the corners - which is why I had suspected my CYA was higher than normal.

I'm still working on understanding what all of you are saying is my third error:
ERROR 3: Lack of either the TF-100 or the Taylor K-2006.

To explain my (probably inexplicable to you) actions, up until today, I was working on the notion that the more complex test kits were mainly for convenience. That is, in over two dozen tests over the past two years at pool stores, my FAC and TAC were always the same numbers. So, I had assumed that with such a low bather load (roughly about 5 to 15 minutes of use per day usually by one bather - the wife) that the basic test kit handled the chlorine levels just fine - and I didn't need to daily test the difference between FC and CC levels.

In addition, no matter which pool store I went to here in the Silicon Valley, the CH, TA, TDS, and (measured inorganic) Phosphates have always been relatively stable, over time ... coupled with the fact that I, myself, had interpretation problems with getting consistent CYA and TA readings using the more complex test kits in the past.

Given those assumptions, I had thought the only three things I needed to test more frequently were the CYA and pH and FAC levels, so, my test algorithm (up until now) was really this simple:
a) Test chlorine & pH daily at home with the basic kit (which works under my assumption that all my chlorine was always available)
b) Have CYA tested monthly at Leslies (noting that all other readings were stable & that my TAC was always equal to my FAC)

However, you're all saying that having the pool store tell me monthly levels is an error on my part ... so my third error must be in not understanding the implied value of doing those rather complex readings on my own on a daily basis ... so I'm re-reading the Test Kits Compared suggestions to see where I err.

 

[duraleigh]

I am such a bumpkin. I always thought Algorithm was a jazz band that the former vice president started up.

 

[rock]

I always thought Algorithm was a jazz band

I'm a Silicon Valley kind of guy - so - we use the word algorithm to indicate our approach to solving problems.

At the moment, I'm trying to figure out the specific value of daily use of the more complex test kits, given that my FAC always equals my TAC and that my pool chemistry is relatively stable in my monthly tests at the pool store and I always had a rough time interpreting the TA and CYA levels using the complex test kits from the pool stores.

So far, it seems chlorine level RANGE & PRECISION might be the (only?) (main?) advantage to using the more complex test kits based on my assumptions below:
a) FC/CC/TC = in my past experience, my pool never has a chloramine problem, so, keeping it simple and not overthinking things has been my "chlorine is chlorine" algorithm in the past. Of course, the basic kit stops at "5-10 ppm" and has no granularity in between.
b) pH = has never been a problem in my experience. My algorithm has been to test daily (simply because it's easy to test pH while I'm testing Chlorine with the basic kit), where I sporadically add muriatic acid if/when needed. However, I never need to add base, and I rarely need to add acid. It might take me an entire year to go through 3 or 4 bottles of 28% muriatic acid.
c) TA/CH/Phos/TDS = has been stable in my experience (as my relatively hard well water is nearly perfect for a gunnite pool and I've never had to add calcium, ever, even when refilling the pool - which I've done twice to date for other reasons)
d) CYA = will remain relatively stable now that I've fixed the leaks and removed the three 3" five-puck floaters

I'm concerned that, everyone here is clearly saying I need the K-2006 or the TF100, yet, after having re-read Test Kits Compared, I must be missing something in applying it to my specific (rather stable) situation.

I've prior concluded that the complex test kits are decidedly not convenient to read - so - they're no more convenient than stopping at Leslies.

Given that, range and precision may be all I get out of the recommended test kits.

That should be enough of a reason, in and of itself, to buy those kits ... but I wouldn't be bothering with 90% of the tests - since they'd read the same day after day after day ... so my confusion about that is why I ask the specific question now of:
Q: In my stable situation ... do I gain anything more than range and precision from the use of the K-2006 or TF100 test kits?

 

[Smykowski]

At the moment, I'm trying to figure out the specific value of daily use of the more complex test kits, given that my FAC always equals my TAC and that my pool chemistry is relatively stable in my monthly tests at the pool store and I always had a rough time interpreting the TA and CYA levels using the complex test kits from the pool stores.

You are forgetting your major (and likely false) assumption that those stable pool store tests are correct. Most pool stores use strips. Just because the strips are read by a computer doesn't mean their more accurate. Or perhaps it's better to say that those fancy computers are really precise in their inaccuracy.

Unless you are fortunate to go to one of the very few pool stores that use a drop based kit, and use it correctly everytime, we just don't trust their results. That's why we use our own.

Plus, then you'll never have to drive there again. I get my tests done in about 3 min over a cup of coffee in the morning.

 

[rock]

Unless you are fortunate to go to one of the very few pool stores that use a drop based kit

Hmmm... I never analyzed exactly what they use, but, it generally takes them about 10 minutes to run my water, and certainly they use drops as I see them put the drops in a tube and run that tube on a shaker - but I don't remember if they also use test strips in addition to drops for some of the tests.

It's only 6:30 am here (California) so I'll call and ask today after they open up and let you know what they say.

 

[jblizzle]

The key to the good test kit is the FAS-DPD test because of the ability to be precise and read up to 50ppm. How do you propose to follow the slam process if your kit only goes up to 5ppm? Just order that test separately then if you think that is all you need. We will still be here when you come back with your next problem.

 

[harleysilo]

CYA testing needs to be done with your back to the sun, with the vial held in the shade of your body, vial held at waist height while you fill it. Does the pool store do that? If not the reading is off by a significant amount.

If that reading is off, and you follow the CYA chart, your target chlorine levels are off by a significant amount.

Perhaps you should take a couple vials of water, say one full of pool water, and what cut by 50% with tap water and do the old switcharoo at the pool store and see how "your firends pool water" scores on their tests....

https://www.youtube.com/watch?v=U_eZmEiyTo0

 

[Bama Rambler]

Even pool stores that use drop based kits are wrong. Don't waste your time. Just go ahead and order a good test kit. If you had gotten a good test kit to begin with you wouldn't be having the headaches you're having now with the algae.

 

[UnderWaterVanya]

Pool store testing accuracy is legendarily bad. Part of this is due to historical use of less accurate methods (strips). Part of this is due to a lack of consistent test procedures across employees, part of this is due to lighting, and part of it is due to the fact that they will offer conflicting advice that does not fit the methods used here.

Test kits that are recommended here aren't hard to use. If you strongly object to the idea you can trust the stores with everything except CYA and FC and maybe get by. You need to test CYA yourself because of the lighting. You need a FAS-DPD test to use the SLAM Process [slam:3cyar9mf][/slam:3cyar9mf]



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