cost/benefit shocking pool

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iam4iam

iam4iam

LifeTime Supporter
May 5, 2012
257
Johnson City, TN
This is my first year as a pool owner. We bought a house last fall and paid the guy who was servicing the then pristine pool to close it. During the month before closing (on the house--which was about the same as the month before closing, since we closed the pool shortly after moving in), the pool was neglected, since apparently they miscommunicated with the pool guy about service. Anyway, he got it looking good again in a matter of days and then closed it. Before noticing TFP, I had already decided to "do it myself" this year and save some money. The pool is 16x32 so I estimate the volume to be 21,000 gal.

Also before seeing TFP, I purchased a load of stuff (online) that now I realize is unnecessary, and some of which is recommended against on this site, for reasons that I think I understand, having educated myself a bit at "Pool School." I'm probably going to pay $20 shipping to return the 50# bucket of trichlor pucks. I'm not even sure I have the heart to try to sell it on Craigslist now after reading "How to Chlorinate Your Pool." I have to note, though, that although this is clearly not biased by selling things, the phrase "very convenient and very insidious" is clearly an opinion. (I probably would lose more than the $20 shipping by trying to resell anyway.) Besides, I could also return the unused stuff in the "start-up" kit (metal out and clarifier) in the same box without adding much to the shipping cost.

I promise I'll get to my question soon. Here's what I've done so far:
When we removed the cover, the water appeared to be in pretty good condition--closer to blue than green, but cloudy. When I got the start-up kit, I added 2 bags of Ca(ClO)2 (just showing off what I remember from 30 years ago in Chemistry class, although I'm not sure I got the subscript right, but I think I know Ca is +2 and I think I remember ClO3 and its "-ite" relatives being -1). I followed the instructions on the bag, which TFP says are wrong, dispersing as evenly as possible by sprinkling in the deep end. I didn't know about the sun's effect on FC, but fortunately I added in the evening anyway, since that was the only time I could. The next morning, FC was at 0 (according to cheap test strip), so I knew I needed to add more, which I did (the other 2 bags that came in the kit), but this time after 2 quarts of 10% alkyl dimethyl benzyl ammonium chloride (algaecide, but I still had the bottle, I figured maybe there are different types and it would help to know what kind I used). What's worse, I added in the morning on a sunny day, so I know that the Cl in that dose did nothing. I also brushed the walls of the pool. I have no idea what effect, if any, the algeacide had. Yesterday, which I think was the day of the wasted dosage of Cl, I stopped by the pool store to get some more "shock" (parentheses indicate that I now know that "shock" is not a noun, but it's way easier to say and I've already identified the type as Calcium Hypochlorite). Last night, I happened upon FTC and didn't add any of the "shock" since I have no idea what my CH level is. Instead, I went to Walmart and bought 4 big jugs (182 oz?) of bleach. I poured 3 of them into the skimmer. An hour or 2 later, FC level was above 0, but not by much, so I dispersed the 4th bottle in the deep end by pouring it in a bucket and throwing it into the middle of the pool to avoid it getting close to the liner. This morning, FC at 0 again with no visible difference in pool water. CYA is in the 30-50 range (best precision I can get with my cheap strip). According to the Pool Calculator, the bleach (6%) should have raised the FC level to about 17ppm, which is shock level for CYA=40. From what I've read, I just need to keep shocking until I see a difference and until FC is present in the morning, which brings me to my real question. The fact that the water is more blue than green (and has been since we took the cover off, or maybe I just don't remember) and the lack of visible difference in pool water makes me wonder if I should just keep shocking, shocking, shocking. After all, bleach isn't nearly as cheap as it was the last time I bought it! Could there be another reason I still can't see the bottom any deeper than 4 ft? If so, is chlorine the answer, regardless?

FYI (just measured prior to posting; lack of precision due to strips):
Ph: low 7s? (appeared to be upper 7s? 2.5 hours ago, a testament to my need to a test kit)
Alkalinity: 80-120
CYA: <30 (although it appeared to be 30-50 range 2.5 hours ago)
 
If you will read "how to shock your pool" in Pool School it will tell you that the correct way to clear your pool is to bring FC up to shock level and HOLD IT THERE until your water is clear.

It is a combination of filtering, brushing, vacuuming and keeping chlorine at shock value that clears your pool.

You also make a VERY good observation....the strips are worthless for proper pool water management.
 
I am a newbie, and I had a pool that was really bad. As a newbie and before I found this site I "shocked" the water and thought that would fix it. What I have learned is that a pool has a lot of water to treat and there is no quick fix, and you need to hold and maintain the FC in the shock level until the water is clear, while running the filter. I have been holding mine at shock level for over two weeks (I also have a lot of sediment on the bottom) and it took a while to get clear but it has worked. I was very frustrated the first week, but it has steadily improved.

Time, bleach, and filtering... hang in there!
 
What they said, well mostly

You seem to have a fair understanding of chemistry even if it is a bit rusty, you will need a good test kit I suggest the TF-100 from TFTestkits mentioned above, it is what I use and while it does cost a little more than the Taylor K2006 kit it is a much better value.

Having said that it is possible to succesfully shock and clear up a pool using a cheap liquid drop based ( either OTO or DPD type, DPD is preferred) Chlorine / pH test available for $10-15 at most pool stores or even Wal-Mart

First take a pool water sample to at least 2 preferably 3 pool stores and get your current levels tested (usually a free service), most important info here is your CYA levels, get numbers, and DON"T follow their advice on what you need, I say 2 or 3 as pool store results are notoriously unreliable, as the test are often ran by minimum wage employees that don't really care about getting good answers.

Buy a drop based chlorine / pH test, before shocking you want to make sure your pH is in the right range (about 7.2-7.5), then you will need to raise your chlorine to shock level and MAINTAIN IT THERE with bleach, the problem is most drop based tests you can buy locally only read up to 5ppm of chlorine and use color matching tests to do this) Since your shock level that you want to maintain will likely be in the 20 - 30 ppm range or higher depending on your CYA level, you will have to dilute your sample down perhaps 6 or 8 to 1 and multiply your reading results to get your true level, this of course also multiplies your error in resolution, and will likely be a bit wasteful in your use of bleach, but it can be done. This is no substitute for a real good test kit, but can let you keep working on it while you wait for the mail to deliver your good kit.

Ike

p.s. note your pH readings will not be reliable while at shock level, it must be tested only when your chlorine level is below about 10 ppm
 
Car guy:
How much bleach have you used?! When you say "holding at shock level" do you mean day and night, or just at night?

Anyone:
How soon after adding bleach should I recheck FC level, how often after that, and where in pool? I still assume that I should be shocking only at night, as trying to maintain shock level during the day seems ridiculous. Am I right?
 
How soon after adding bleach should I recheck FC level, how often after that, and where in pool? I still assume that I should be shocking only at night, as trying to maintain shock level during the day seems ridiculous. Am I right?
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You are partly right.

You should check the FC level and redose usually within a couple of hours after the first dose of chlorine. The first dose gets consumed VERY quickly (usually) and the whole idea is to maintain a constant level of shock value chlorine for the duration of the process. A typical process might go like this...

Dose to 20ppm (CYA=40). Check two hours later FC = 12ppm...dose enough to get back up to 20ppm. Check 4hours later.....FC = 12ppm....dose enough to get total FC back up to 20ppm. Check just before dark FC = 8ppm dose again to get total back up to 20 etc. etc.

You will certainly lose a lot of FC during the day especially if you have no CYA but, if time permits, you will complete the process quicker if you will test and redose as often as you can.

It makes no difference where in the pool you take your sample. Distribute your dose directly in front of a flowing return so it is immediately diluted.
 
You should not stop while you are shocking, think of this as a war against algae, and the algae can breed and replace itself at an incredible pace particulalry during daylight hours. If you were to shock only at night you give the algae all day to breed and you will never win. This is why it is so important to not stop shocking until you get all the algae otherwise it will be back at full force in a few days.

Ike

p.s. I am going to partly disagree with Dave here, you want to take your sample in a place where you know there is water flow, I was helping someone gain control of their pool around here a few years ago, and they always took their samples at the alcove steps due to the easy to grab handrail, unfortuneately this alcove step area did not get good water circultion and could differ by 2 or 3 ppm on free chlorine compared to samples taken elsewhere in the pool.
 

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Is this a bad idea?
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Not quite as good of an idea as directly in front of the return. If you pour the bleach into the skimmer slowly, then it's fine but poured in quickly, you put a really high concentration of chlorine going through the equipment. It probably doesn't hurt much but it is in the long term harder on your equipment than letting it go into the return stream and getting it very diluted before it gets pulled back into the skimmer.
 
duraleigh said:
It probably doesn't hurt much ....
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Are you just trying to console an ignorant beginner (which I appreciate)? Have I essentially subjected my equipment to the "danger" that is why we don't just shock the heck out of our pool without a "goal" level and no fear of too much chlorine? (And by the way, it was a rather fast pour--about as fast as the jug would allow.) Actually, I mentioned pouring directly into the skimmer in original post, but I also said a lot of unnecessary stuff, so I'm not surprised no one advised against it until now. (I added another dose into the skimmer before asking if this was a problem. I'll not do it again.) That being said, an hour after the dose the FC was still below 5 (hard to read since I was expecting a number over 10 and diluted 2:1 to get a reading, but the "diluted" reading (using test strips still) was small enough that x3 would still be probably < 5. Did it just not have enough time to circulate through the equipment and back into the pool? I added some more (50% of original evening dose) in front of a return. I might not get much sleep tonight! I can hardly fathom how much bleach it will take to maintain shock level during the day (and the cost)!
 
The greater cost is when you don't maintain shock level think of it like this: (these are not actual numbers, just a represenations) Chlorine kills 10% of algae every hour it is maintained at shock level, algae doubles its number every 4 hours not at shock level in daylight, start with an algae load of 100

You shock for 6 hours adding bleach as needed every hour or two and get algae down to a level of 40, then take a break duriing the daylight hours while you go to work for 8 hours, after 4 hours the algae is now up to 80, after another 4 hours it is at 160 which means that 8 hour break has put you back to a point worse than where you started from and all that bleach was wasted.

Your goal needs to be maintain shock level until 100% of the algae is DEAD every time you let the chlorine level drop below shock level your taking a step backward, or at least are fighting to a draw.

Ike
 
I follow what Isaac-1 is saying mathematically and understand the point he's trying to make. I know the numbers are "representative" only, but I cannot imagine that algae grow 2.5 times faster with FC not at shock level than they are killed when it is at shock level. If this were true, my pool would be a swamp by now. It actually looks very similar to a week ago when I took off the cover, maybe slightly better, even. At this point my main frustration is that I can't even get the FC to shock level to begin with! I've added 20x96 oz of 6% since dark (including 10x96 oz into the skimmer which I realize now was not the best move) and still haven't had a reading that's clearly over 3 ppm FC. (I just took a reading using the dilute idea since I keep expecting a number > 10--granted, using a test strip. I know strips aren't the most precise measurement out there, but it's not going to be barely gray when it should be dark purple! CYA is definitely below 30 according to strip, from which it reasonable to conclude that it's not over 50. That being said, unless I don't understand, CYA level affects the effectiveness of the chlorine, but not the actual FC level! I'd just like to get to shock level, but I've already used $30 worth of bleach since dusk and I'm nowhere close! This can't be right!
 
Your experience is pretty much why no one here uses test strips. They are a waste of time. If you really want to understand what is going on in your pool, you will sooner or later have to get a test kit that will help you....not mislead you.
I can hardly fathom how much bleach it will take to maintain shock level during the day (and the cost)!
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What is your alternative? You have to get your pool cleaned up (I think) and bleach is either the cheapest way to do it or darn close to whatever else might be in your area.
 
Ok, there are a couple of possibilities here:

The test strip is giving you a false reading, cheapest way to determine this is go buy a cheap drop based OTO chlorine /pH test usally $10-$15 at Wal-Mart (try not to get the slightly more expensive DPD test at this time as it can be "bleach out" at exteme chlorine levels). The problem with the OTO test is it can't reliably measure over 5ppm of chlorine, you will get some extreme orange color off the top of the color scale though. From there you can try to determine the ballpark of your actual chorine level by diluting the sample with chlorine free water (distilled is the best bet) and multiplying your results by the dilution raio, this of course also multiplies your uncertainty in matching the color, but gets you in the ballpark.

The second option is the test strip is telling you the truth and you have something consuming vast amounts of chlorine, if this is the case my guess is you have / had ammonia producing bacteria in the pool, it takes vast amounts of chlorine to neutralize ammonia, and the reaction byproducts are not all that nice.

Ike

p.s. the sooner you throw out the strips and buy a good test kit, the sooner you will stop feeling so frustrated
 
Thanks for the suggestions. Given that I do not believe the test strips could be giving me readings that have 150% error, scenario 2 (ammonia) sounds more likely, albeit much more scary. Is there any way to know if this is the case? If scenario 2 is the case, do I have other options than to use $500 worth of chlorine?

By the way, while I plan to invest in a real test kit and understand the inferiority of test strips, a test kit will not help me get my FC to shock level. It will just give me a more precise reading as I approach that level and when I get there. I am not frustrated by not knowing how far I am from shock level. I am frustrated by not being close after 2 times as much chlorine as it should have taken to get me there! While a test kit might tell me exactly when I get to shock level, unless a test kit will tell me exactly why I cannot get there, it will not end my frustration.
 

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