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/showthr...5545#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

[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