Turning a green pool blue again

How to Shock a Swimming Pool

(Continued below…)


                It’s finally published!!!

A funny, inspirational story of growing up in America, finding God (or being found BY Him), written by yours truly!  Replete with humor and honest insight…


Into the Cross-Walk, by BIC (actually Bic is just my pen-name; my real name is Mark). 




Available in the following formats:



Paperback at Amazon

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Download a sample chapter here (pdf) or view here (as a web site)



About me:

Mark graduated in the top 1% of his 5A high school class, is a certified ASE mechanic, and once held a medical degree before the doctor told him to put it back on the wall.  Mark is a devout born-again Christian who has perfected his own recipes for home-brewed coffee and all-grain beer, and has been playing the bass guitar since 1984.  Besides writing, he is an avid programmer, a dog lover, has a really cool car and likes to start lots of interesting hobbies, and then abandon them.



Turning a green pool blue:

I’ve gone through this for the first time, and wanted to document how to do this right, omitting all the stupid mistakes that I made, both for myself and anyone else, so everything is in one place.  First of all, for the pool setup, this year I installed a skimmer and I took my good sweet time slowly adding water, adjusting the liner & such so it would be centered (was a little off last year & some of the poles popped out), and raised the level up to just about where my new skimmer would go.  The pool is an Intex 6300 gallon 18’ metal-frame, now with a Hydro-tools skimmer and a 2650gph Intex 100lb sand pump.  All upgrades I would highly recommend.  I also built a deck and my own PVC ladder.

However, taking so long to fill the pool, by the time I got all that work done, algae had taken over completely.  Instead of listing what I did, I’ll list the proper steps to bringing the pool back to sparkling blue.

Part “A” – shock that pool!

1.       Read everything you can at www.troublefreepool.com, especially pool school (http://www.troublefreepool.com/pool-school/) and the “BBB” method (http://www.troublefreepool.com/pool-school/bbb_for_pools) which basically means you’re going to use inexpensive stuff to treat your pool (Bleach, Baking soda & Borax). 

2.       Buy a decent test kit.  I got one of these:


You’re going to have to shock the pool – bring up the free chlorine really, really high – and standard Walmart test kits don’t read high enough.  It’s also (I’m told) more accurate than the free testing they do in pool stores.  Besides, every time they give you a “free” test, they try to sell you something, which is very annoying.  When you buy the kit, you can add other stuff in for a discount, so if you have a saltwater chlorine generator, be sure & get some salt test strips too.

3.       Read how to shock your pool (http://www.troublefreepool.com/pool-school/types_chlorine_pool ).

4.       Buy a LOT of plain, unscented, inexpensive bleach.  Walmart in my area has 182oz “Great Value” bleach (active ingredient 6%) for $3.  Getting rid of algae is all about using the active ingredient in bleach (a form of chlorine) to “eat” the organic matter in the pool, which includes Algae, leaves, combined chlorine, bugs – everything that makes it cloudy and gross.

5.       Once the pool is full & ready to run, start the filter pump up & make sure it’s working OK (check for leaks, etc.)  Back-flush if necessary.  Let the pump run for several hours to get things circulating.  If you use a salt-water generator usually, leave it off for now.  There’s no way it’ll be able to create enough chlorine to get rid of algae.  Once the pool chemistry is right and the pool goes from repulsive to inviting, then it’s time to use the saltwater generator to maintain the chlorine level.

6.       Vacuum or skim the leaves out as best you can.  You can’t see them, but they’re there.  In my case, with a circular pool, they formed a mound in the middle of the pool.  For days I thought it was just a big shadow; it wasn’t.

7.       Take out your brand-new little chemistry kit and follow the directions to measure free chlorine (FC).  Don’t use the “daily” test – use the other one where you count the drops and swirl the sample around.  In all likelihood, it’ll be zero or almost zero.  Make sure you sample about 18” below the surface, after the filter has been running for a while.

8.       Measure your cyanuric acid (CYA) with the test kit.  You might want to run the pool water sample through a coffee filter first; there’s some debate as to whether this affects the accuracy of the test, but in any case, it can’t hurt.  This is the test with the black dot at the bottom of the tube; you want to add drops per the directions until you can’t see the black dot *at all*.  Best done in indirect sunlight, and don’t mistake the bottom of the tube for a dot.  Repeat this test if you’re not sure.  It’s important to nail this number.  If you just filled your pool up, this number will be really low or zero.

9.       With FC and CYA numbers in hand, go to CYA/Chlorine chart:


Find your CYA level (let’s say it’s 40) and the corresponding FC level to shock it (16 for a CYA of 40).  So let’s say your target FC to shock the pool – which means get rid of the algae and all the other gunk in there so it’ll be clear blue instead of sludge – is 16.

10.   Pull up the Pool Calculator:


and start putting in numbers.  First, put in the size of your pool in gallons (you can also use metric units if you change it, at the top of the form).  I was able to figure out the gallons from the pool manual, since I have a manufactured above-ground pool; there’s a section further down that will calculate it based on dimensions.  Then fill out the FC level in the “Now” section that you measured (say it was 1.5) and the target section (in this example, 16).  Press the TAB button or click on another field, and the calculator will show you how many ounces of bleach you need to add to the pool, to achieve a “shock level” of 16.  Look on the bottle of bleach, for the active ingredient; the Walmart brand is 6%; you may have to change this number based on what you bought, and that will change the number of ounces.  In this example (6300 gallons, FC of 1.5, target of 16, 6% bleach) it recommends adding 189 ounces of bleach.  Remember that number.  (You can also mouse-over the “ounces” and it’ll convert that into gallons/quarts etc. at the top).

11.   Back outside, grab your bottle of bleach, and measure out the bleach (189 ounces).  Pour it into the stream of water coming from the filter back INTO the pool; do NOT pour it into the skimmer or the pump suction.  Pure bleach can attack the pump seals & gaskets & you’ll end up with a leak.

12.   Let the filter pump run for a couple of hours, then re-test your free-chlorine (FC) level.  You may have to adjust your bleach use up or down, based on the FC level.  If it’s too high, then put less bleach in than the pool calculator says (or decrease your pool size).  If it’s too low, then put in more (or increase your pool size in the calculator).

13.   The idea is to never let the FC level fall below shock level.  In my case, I have a job.  I can’t baby-sit my pool during the 12 hours it takes to go to work & come back, or overnight when I tend to sleep most, so what I did is measure the FC level in the morning, then again in the evening.  I found it was dropping by about 7 during the day.  So, I adjusted my target upward: instead of shooting for a FC level of 16 in the morning, I shot for 23.  That way, through sunlight and the hungry chlorine eating up all my pool’s filth, it was still above shock level (17 or 18) by the time I got home.  If it falls below shock level, you’re just wasting bleach, because the algae will start coming back again.

14.   Every day, brush and/or vacuum your pool, and check your filter.  Back-flush or clean your filter media as needed; it’s going to be picking up a lot of stuff, and may need to be flushed every day or two.  Measure your FC at least every morning & evening, plug that number into the pool calculator, and add bleach as needed.  Your filter pump should be running 24/7, unless you’re servicing it.

15.   If you don’t have a pool brush, you can go to the pool store and buy one.  Don’t tell them what you’re doing.  They’ll just start in with “bleach is going to ruin your pool” or “never listen to those trolls on the Internet!” or “this bag of chemicals is what you really need…”  Just buy your stuff, smile, and leave.

16.   Create an account at troublefreepool.com and start a topic if you have any questions, or just want to introduce yourself.  These guys have helped me out tremendously, they know what they’re talking about probably more than any of your local pool stores, and they’re not trying to sell you anything.  They can give you hints & tips (that’s where I got all of this information) and help you if something comes up.

17.   Be patient.  It can take two weeks or more to clear up the water, especially if you use a sand filter.  Cartridge filters & DE filters are faster, but patience is still required.  If you have a sand filter, and want to speed up the process a little, you can get some diatometrius earth (DE) from the pool store, or I even saw a box of it at Walmart.  Instructions for adding it are here:


although, sand filters work just fine as long as they are properly backwashed when the pressure rises (or the flow drops off) and you put them on “rinse” for a full minute after the backwash to pack the sand back in.  If there’s any doubt, you can always open up the top & inspect the sand.

18.   You’ll know when the chlorine is done doing its job when the FC drops by 1 or less overnight.  At that point, you will find you’re adding less bleach and basically waiting for the filter to finish clearing the water.

19.   There’s a second part of the FC test that I didn’t mention before.  One of the things you’re getting rid of with all this chlorine is “combined chlorine”.  It’s present whenever the free chlorine is “combining” with something nasty.  Start testing for combined chlorine levels once your water starts to clear up.  Instructions on testing for CC are listed in the test kit; you test for FC, then follow the directions to continue (with the same sample) & test for CC.

20.   You are DONE shocking your pool when the water is clear, you lose 1 ppm of free chlorine (or less) overnight, and your combined chlorine (CC) is 0.5 or less.

If the FC ever falls to zero, or your CC goes above 1.0, you may want to consider shocking the pool again.  Some people even shock the pool after a big bather load (kids’ birthday party) or a heavy rain.  In any case, with the pool now clear blue instead of cloudy green, it’s time to fine-tune it.


Part “B”: Get the chemistry right!

It took me 18 days to get the water crystal-clear, and pass the OCLT (overnight chlorine loss test), but it’s done.  The next thing to do is check the water for all of the other parameters.  Your target will depend on whether you’re running a saltwater generator or not.  If you are, like I am, then your chemistry should look like this:

PH 7.5-7.8

TA (Total Alkalinity) 60-80

CYA (Cyanuric Acid) 70-80

Salt: per your owner’s manual

FC (Free Chlorine): 3-5 ppm

Note that at this time, the salt-water generator is NOT running.  I didn’t want to turn it on until everything was perfect, or at least pretty close.  I also constantly checked the chlorine level; I didn’t want it to drop back to zero.  It was at 18 or so after shocking, so by the time the chemistry was right, it was down around 6 or 7.

For me, the pH was low, so I used the Pool Calculator to calculate how much Borax to add.  Borax is an old-fashioned laundry booster, made by “20-Mule Team”.  I found it at Walmart in the laundry aisle.  I poured it slowly into the skimmer, let the pump run all night to get it into the water.  If the pH was high, then I would have added Muriatic Acid, available in the paint department at Lowes or Home Depot, or at the pool store, but NOT into the skimmer.  Acid is bad for pumps, so I would have poured that into the water jet going back into the pool.

TA (Total Alkalinity) is supposed to help keep the pool chemistry stable, mainly the pH.  Mine was low, so I added some baking soda, again, into the skimmer, per the Pool Calculator, and let the pump just run & run & run.  (I started to feel sorry for the poor thing – it must be getting tired.)

CYA (Cyanuric Acid) is very important for salt-water pools.  Its main purpose is to prevent the chlorine from being eaten by the hot sun, but it also stabilizes the salt cell so it doesn’t burn itself out.  Adding CYA is tricky; if you buy some from the pool store, it’ll come in granules.  If you dump that into the skimmer, it can solidify and completely plug your piping.  It has to be released slowly into the water.  I poured mine into an old sock, hung it over the side of the pool for a few hours, then put it in the skimmer.  I’d go give that sock a squeeze every now and then to help it along, and after another day or so, it was all in the water.

CYA also has a tendency to lower the pH; my pool had been at 7.5, and went down to 6.8 after the CYA dissolved.  So, more Borax.  No big deal.  Actually, Borax is good for the pool water.  Makes it silky-smooth and shiny.

The last thing to check is the salt content.  I already had salt in the pool; I checked it, turned out to be 2800 (3000 is “perfect” for my Intex CS8110, but 2800 ain’t too bad).  So, I set the pump to run for 4 hours.  I started the pump, waited about 30 minutes, then started the saltwater generator to run for 3 hours.  I figured that was a pretty good starting point.  You’re supposed to run the pump long enough to change out the water daily; mine is rated at 2650 gallons/hour, so to change out a 6300 gallon pool would be at least 2.5 hours.

Part “C”: Maintain beautiful pool water!

After all of that hard work, I didn’t want to take any chances that the pool would get out of control, algae would return or even that the water wasn’t perfectly safe for my wife & kids.  So, instead of just being blissfully ignorant like I was last year, I got into a daily routine:

1.      Clean out the skimmer basket

2.      Take a sample & check the pH and Free Chlorine.  Adjust pH as needed with Borax/Acid, and increase/decrease the saltwater generator run time.

3.      Check the pump pressure, back-flush if necessary

4.      Check the pool for debris, vacuum if necessary

Then every week I would run a full chemistry check: Free Chlorine, Combined Chlorine, Total Alkalinity, CYA, pH.  Adjust as necessary, and put a big “Pool Closed” sign on the back door until everything is OK again.

Every few weeks I remove the salt cell from the chlorine generator, cap one end, then fill it up & let it soak in a 50/50 mix of muriatic acid and water for 30 minutes or so.  That keeps the cell nice & clean so it’ll always make lots of beautiful chlorine (gets rid of scale build-up).  I also take the opportunity to check the salt level, and add salt as needed.  The salt level will naturally go down as rain & splashing displaces the pool water, so it’s just an ongoing process.

That’s about it!  I can’t recommend the guys at www.troublefreepool.com enough.  They are very helpful, experienced pool enthusiasts, and they cover just about every pool topic imaginable.  I highly recommend their Pool School; it seemed overwhelming at first, but just like everything else, if you want it done right, you have to learn how & then do it yourself.