Pool Store vs Test Kit Results??

[hawkeye91]

Hi everyone -

This is my first post after doing a lot of reading here this weekend, and I have to say, the support and knowledge here is incredible! The BBB method seems easy to follow, and I'm slowly digesting the relationship between the different chemicals and test levels.

What brought me here in the first place was some yellow algae that has formed on the walls of the pool twice in the past few weeks. Having successfully addressed it now for the second time (thanks to advice here) I've come to the realization that I have never, in the 2+ years that I've had the pool, given the chemistry the attention it deserves. I just did what the pool store said - "shock it once a week and use these pucks." Sound familiar? =)

So, I want to make a conscious effort to keep things more in line, but, as my title implies, I'm struggling to reconcile differences between my test results (strips and hth kit) and the pool store's testing


The vitals...

Pool is 9800 gal. in-ground, white plaster.


My results using test strips...

TC = 10 (scale only goes up to 10)
FC = 20 (scale goes up to 20)
pH = 7.8
TA = 120


My results using hth test kit...

CL = 5.0 (scale only goes up to 5.0)
pH = 7.6
TA = ?? (not sure how to measure using this kit - no instructions)
CYA = 60


Pool store results...

TC = 4
FC = 4
pH = 8.2
TA = 140
CYA = 97

All testing took place this morning, and now I'm thinking "what the heck?" To me, these are drastic differences, but is this typical to see across the different methods?

I'm tempted to think that the test strips are junk. I'm also tempted to think that the hth kit is junk, because it suggested all along that the cholrine level was fine - and then the algae appeared! That leaves me with the pool store which I'm (uggh) tempted to believe since they didn't try to sell me everything under the sun based on their results. But I don't want to have to rely on them for regular testing.

So, which do I believe, and what do I do next? If I follow the hth kit, I'd leave things alone for now, but if I follow the pool store, I'd add both bleach and muriatic acid. In the end, all I want is something I can trust. Maybe I just get the Taylor kit and start over (so to speak)?

Thoughts?

Thanks all!

Scott

[aylad]

Hi Scott, and welcome to the forum!!

First off, I would junk the test strips. They are sometimes useful for indicating the presence of or absence of something, but they are not accurate and consistent enough to base your treatment of water problems on. You definitely need to use a drop-based kit. I very strongly encourage you to get the Taylor K-2006, which will completely eliminate the guesswork and make taking care of your pool SOOOO much easier!! The Taylor can be purchased online through this link http://www.poolforum.com/pf2/showthread.php?t=10006 (and PF gets a donation from them when you use that one!) or also at www.sps-poolsandspas.com.

So, in throwing the test strip results out, you're left with the HTH or pool store readings. The chlorine readings are not that far off, so I have no argument with them. Regarding CYA, now there's a big difference--but I'll tell you that if your CYA is 60, the 5 ppm is the absolute LEAST level that you can let your chlorine drop to. If it's 97, then you need to keep the chlorine no less than 8 ppm...so either way, you need to up your chlorine some, if you're having problems with recurrent algae.

I would shock the pool based on the 97 reading, using plain, unscented bleach, and hold it at shock level by testing 2-3 times daily and adding more bleach to get back up to shock level, which will be 25 ppm. In a pool your size, each 3 cups of 6% bleach will raise the FC by 1 ppm. Hold it at 25 ppm until you're not losing any chlorine overnight when testing at night after the sun is off the pool and testing again in the morning before the sun is on the pool. Then when you let it drop back down, don't let it get below 8 ppm. In the meantime, you'll have time to order and get your new kit, and then you can go from there, using numbers that you know are accurate!

By the way, no trichor pucks or dichlor shock for you--that's going to raise your CYA even higher. Also, it's a plaster pool--you didn't list a level for Calcium hardness, but you need to have that in the 200-400 ppm range....

Janet

[hawkeye91]

Hi Janet --

Thanks for the information - I'm definitely going to get the Taylor kit today!

Now that we've scrapped the test strips, nothing I currently have will allow me to measure the chlorine above 5 ppm. I believe I've read that the Taylor kit will allow that, but I'm not sure how to attack the shock process in the meantime. Unless you have some ideas, I'll just make sure it doesn't go below the 5 ppm with the HTH kit until the Taylor kit arrives.

The hardness is not good - 560 - but about all I can do about it right now is drain and refill a couple of inches of water at a time (which I know is almost worthless). I don't have the means to drain and refill the entire pool quickly, and everything I've read suggests that the plaster will bake and be destroyed if I try. So I think I'm stuck with that until it cools off, which here is about November!. =)

Scott

[aylad]

Here's how to force your HTH kit to measure chlorine higher than 5 ppm....
http://www.poolforum.com/pf2/showthread.php?p=65545#post65545

Hardness isn't that bad at 560, just watch for scaling. Depending on the hardness of your fill water, it's possible that if you drain/refill just part of the pool, it'll bring it down into the recommended ranges--and that will also drop your CYA down into manageable levels, too.

Janet

[Watermom]

Hi Scott and welcome. Janet has given you some good advice and yes, you need to order the Taylor kit. Glad you found us!

[hawkeye91]

Janet / Watermom -

Thanks for the help. After a couple days' work, here are my numbers from this evening...

FC = 9
pH = 7.4
TA = 125

I'm going with the assumption that the pool store CYA of 97 from above is accurate until the Taylor kit arrives and I can retest that. So...

I kept FC at 25 all day yesterday (Monday). There was no FC loss overnight last night, so I allowed it to fall during the day today. Since the pool was not usable anyway, I decided to go after the TA as well, so I added acid to drop the pH to 7.0 and then aerated all day yesterday. The water is crisp and clear, and I'll keep aerating until the pH is around 7.6, and keep ratcheting down the TA over time too.

I have two questions at this point...

1. What is the best approach to maintenance? Since we know the FC will burn off in the sun, do I add excess bleach in the morning, so that when we're ready to use the pool in the evening, FC is around 8? (like most folks here, I can only test early morning and at sundown on weekdays)

2. I guess this is related to #1. I've read elsewhere on here that FC = 10 is pretty much the upper limit to allow swimming, but I need to keep mine at 8. That's a pretty narrow margin. I'll keep trying to lower the CYA by replacing water little by little over time, but if you have any tips on how best to maintain 10 > FC > 8 that would be great.

Thanks again!

Scott

[Watermom]

The best time to add chlorine is in the evening when the sun is off the pool. By doing so, you have all the chlorine available to sanitize the water instead of having it lost to the sun. If you are not losing chlorine overnight, then you'll still have the same amount of cl during that day to work in your pool. If you do lose more than 1ppm of cl overnight, then you need to add bleach in the a.m. as well.

You don't have to have the cl between 8-10 to swim. When we tell people they want the cl below 10 to swim, those are people who have much lower cya levels than you do. With high cya, it is ok to swim at higher cl levels than with lower cya. So, with a cya of 97, it is fine to swim when the cl is 8-15 although when it is in the upper area of the range, you would probably want to wear old suits.

Hope your kit comes soon so we'll know for sure what your cya level is. Hope this helps.

[CarlD]

It's great to see a newbie doing everything right! Usually, we all make super-duper mistakes at that time.

Jan and Lisa have guided you correctly.

Until you get the K-2006 you can dilute pool water with distilled water (the "CarlD Patented Shot Glass Method") to boost the range of your HTH chlorine tester.

I like the shot glass because it's not too big, not too small and gives VERY precise dilution. So...1 shot of pool water and 1 shot of distilled water mixed together, then poured into the test block (or "cell") will allow you double the reading you get. If it reads "4", your chlorine is 8.

If you use 2 shots of distilled to one of pool, you triple the reading--therefor if it reads "4" it's really 12.

Hope this helps.

[hawkeye91]

Thanks Carl.

Still no Taylor kit -- hoping for early next week. For now the shotglass method is working just fine. My only concern is that I am -- or at least it seems to me like I am -- using a lot of bleach. The FC is degrading at a rate of about 9-10 ppm per day, so I'm adding a full 182-oz bottle everyday.

I suppose it is what it is, but is this typical/normal?

Scott

[Watermom]

Can you post current water testing results? The last ones posted are from a couple of days ago. Losing 9-10 ppm of cl per day is a lot. Are you losing more than 1ppm from sundown to sunup? How does the water look?

[hawkeye91]

Hi everyone --

Got my Taylor test kit today - here are the results from tonight...

pH = 8.0 (has been 7.5-7.6 with HTH kit for days)
Acid demand = 3 drops
FC = 6.4 (was 15 this morning with HTH kit)
CC = 1.0
TA = 125
CH = 700 (!??)
CYA = 60

Based on a CYA of 60, a FC of 6.4 would be right in the middle of the ideal range per the best guess CYA chart. Would that be high enough to throw the pH off, or is the 8.0 likely valid?

Scott

[Watermom]

A cl reading of 6.4 should not affect pH readings. With a CC reading of 1.0, you are fighting something in the water and need to shock this pool and try and hold the cl at shock level until you can go from sundown to sunup without losing more than 1ppm of cl. Run your pump 24/7 for now. Wow! CH of 700? No using cal-hypo in this pool. Also, with a cya of 60, you don't want to use any trichlor pucks or dichlor powder. They will make the cya go up and you don't want it any higher. Stick with bleach.

How ya like that new kit?

[hawkeye91]

Love the new kit! It will be much easier to get a handle on things now. Of course I don't need to tell you that. =)

Morning numbers...

pH = 8.0+
Acid demand = 3 drops
FC = 6.0 (so lost 0.4 overnight)
CC = 0.5

I added acid this morning, but no bleach because I wanted to get a true picture of what was going on with the FC/CC.

Evening numbers...

ph = 7.5
FC = 4.0 (so only lost 2 ppm during the day as opposed to the 9 that the HTH kit was reading - what a piece of junk!)
CC = 0.5

I'm definitely going to add bleach tonight, but do you still think I need to bring it up to shock level, or just bring it up to 10.0?

Thanks!

Scott

[Watermom]

I think if it were my pool and I had a CC reading of 1 less than 24 hours ago, I'd go ahead and shock it up one more time. Then, if you still have less than a 1ppm loss overnight, then let it drift down and I think you'll be good to go. (You are probably ok not to shock, but it is just kind of like insurance. Won't hurt.)

[hawkeye91]

Makes sense, so I added enough bleach last night to increase the FC to 18. This evening's results...

FC = 10
CC = 0
pH = 7.9
TA = 110
CYA = 60

I was unable to test this morning, so I'm not sure how much FC was lost overnight versus how much was lost during the day today.

I biffed on the pH -- added some acid to drop the TA and aerated at the same time. I've since read in a couple of posts that I should have dropped the pH first, and then aerated which I will do from now on. But it does bring up a couple of interesting questions...

1. The Taylor book says that the pH reading should be accurate as long as FC is 10 or less. Do you find that to be accurate? Since I'm right at 10, could that be causing an artifically high ph?

2. Any idea how quickly aeration increases pH? I added enough acid last night to drop it to 7.2 so something seems a bit off here. At least I dropped my TA by 15 points. =)

I know I should probably only tackle one adjustment at a time (yes, I'm certain I learned that in chemistry class a long time ago); but, the trial by fire has been kinda fun.

Scott

[aylad]

I have measured accurate pH with chlorine levels higher than 10 with a very similar kit to yours (that uses Taylor reagents), so I think that you're probably getting an accurate pH reading with your chlorine at 10. As far as how quickly aeration raises pH, that depends on the pool and the amount of aeration (and some on the level of TA itself). A waterfall would definitely raise pH by aeration quicker than a return pointed upward. I find that a pool full of 10-year-olds raises it rather quickly! :)

Janet