my awful trip to the pool store

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Only tests I casually trust the pool store with are TC, pH, and TDS. Only because they use the same simple OTO kit we have. And TDS.... well I guess it really isn't too important if it's not even included in Dave's or Ben's kits. It's nice to know a ballpark figure though.
 
You can very reasonably estimate the TDS by simply adding up the individual components (I use the CYA adjustment factor to alkalinity at a pH of 7.5).

TDS = CH * (40/100) + (TA - CYA/3) * 2* (61/100) + CYA * (128/129) + Borates * ( 61.8/10.8 ) + Chloride(Salt) * ( 35.5/58.4 ) + Sodium
TDS = Calcium + Bicarbonate + Cyanurate + Borates + Salt

All of the above except for "Sodium" is taken directly from the ppm measurements including a salt test (which actually measures chloride, but is reported as "ppm sodium chloride"). The Sodium is figured from charge balance:

Sodium = 23 * ( (TA - CYA/3)*2/100 + CYA/129 + Chloride/58.4 - 2*CH/100 )

In fact, since most other junk in the pool such as dissolved organics are very small in quantity and are often neutral in charge, the above will be even more accurate than a conductivity test used for TDS. Also, note that the conductivity test will not measure the Borates for TDS since Boric Acid is the main species and it is neutral.

Looks like the above is one more thing that could be put into the online pool calculator -- probably one that calculates the saturation index since similar input parameters are used for both.

Richard
 
chem geek - What is the formula for calculating CSI? That would probably be far more useful than TDS. Actually, I don't know of any use for a TDS number, except perhaps to see if it differs from the equation you just gave indicating that there are other things in your water that you don't know about.

It looked like you were about to talk about CSI in this thread, but then you didn't.
 
A very close approximation to the accurate Calcite Saturation Index uses the following formulas (I do refer to these in that post, but in the spreadsheet itself, not in the text of the post):

LSI = pH - 6.9395 + log(ppm CH) + log(ppm CarbAlk) - 2.56*sqrt(I)/(1+1.65*sqrt(I)) - 1412.5/(oC+273.15)

I = (1.5*(ppm CH)+(ppm TA))/50045 + (extra NaCl ppm)/58440

[EDIT2] I removed the 1.290 factor on ppm CYA [END-EDIT2]
extra NaCl ppm = TDS - ( 1.109*(ppm CH) + 1.679*(ppm CarbAlk) + (ppm CYA) ), but if <0 then use 0

[EDIT] I've added a Borates correction to the following [END-EDIT]
[EDIT2] I changed the "6.88" to "6.83" to account for typical ionic strength at TDS from typical CH and TA with no extra salt [END-EDIT2]
ppm CarbAlk = (ppm TA) - 0.38772*(ppm CYA)/(1+10^(6.83-pH)) - 4.63*(ppm Borates)/(1+10^(9.11-pH))

[EDIT2]
If one uses a salt measurement (which measures chloride and reports as ppm sodium chloride) instead of actual TDS, then the formula for extra NaCl ppm is as follows:

extra NaCl ppm = Salt - 1.168*(ppm CH), but if <0 then use 0
[END-EDIT2]

The "log" are logarithms to the base 10 (i.e. they aren't "ln"). So start with the bottom formula and work your way up. So first calculate CarbAlk using TA and CYA. Then calculate the extra salt via the TDS, CH, CarbAlk just calculated and CYA. Then calculate the "I" which is the ionic strength using the CH, TA and extra NaCl (salt) that was calculated. Finally, the LSI is computed.

Obviously, the above is best done online, or in a spreadsheet, or in a program. Michael Smith can add this to BleachCalc and you can add this to your online calculations. It will be close to, but not the same as, the Langelier Saturation Index (LSI), but will actually be more accurate. It seems to be virtually the same as the Taylor Watergram wheel except at very high temperatures above 120F and even then the error is small. You'll need to convert the temperature from Fahrenheit to Celsius but that's just oC = 5*(oF - 32)/9. The LSI as used by the pool industry is actually incorrect and uses logarithms for the temperature and TDS portions of the computation when they should have used the formulas I showed above, but then they were trying to simplify things though the temperature formula isn't complicated so I'm not sure why they went with logarithms for that except to "appear" consistent with all factors except for pH (which is already a logarithm).

Richard
 
First off...I laughed my head off reading the rest of the responses to this thread so much that I had to forward it to my sister after she had to listen to all my venting on this issue. The ridicule from my neighbours and looking over my shoulder for the rest of my life does really concern me too ;)
On a more pertinent note my FC levels held at 3 over night last night and dropped to about 2 over the course of the day. The water reamains cloudy but I think it's clearing. PH 7.6 TA 90. I added enough bleach (I'm hoping) to raise it up 1ppm vac. in the a.m. and just swept it after adding the bleach. So...how patient do I need to be about my water clearing? It's remained at pretty much this state since tuesday. There still appears to be some piling of what I'd guess to be dead algae along seam lines and beneath my return in the deep end of my pool.
As for the TDS calculations...I'm not sure yet what that is...guess I can look that up and learn myself. But even my top secret chemistry numbers from the pool store didn't include this.
Thanks again for the advice and even more so for the laughs :)
N
 
TDS stands for Total Dissolved Solids. It's essentially a measure of everything that is dissolved in the water (except the water itself). It's usually measured using a conductivity meter which means that this method is only going to measure things in the water that are charged. One is supposed to use tables or a calculator to input known values for the main components of TDS, namely CH and TA, and then it is assumed that the rest of the conductivity comes from salt.

But as has been said before, TDS is really bogus in that you don't need to worry about it AT ALL. It does somewhat affect the saturation index, but really only if you have a salt pool (3000 ppm salt which is around 3200 ppm TDS). Other than that, it's absolutely nothing to worry about.

Richard
 
Congratulations on the FC holding!

It will probably take some vacuuming and several days for the pump/filter to completely clear the water from this point. You should see a clear improvement each day from here on.

Don't worry about TDS and all that other technical babbling, you don't need to know anything about any of that.
 
Alright...I'll try to remain patient. My pump's been running 24/7 for weeks now trying to clear it all up...I guess a few more days won't hurt...just paranoid about the algae returning I guess.
I actually enjoy the technical babble...in fact for years I paid to have people technical babble at me. Thanks for the explaination.
N
 
If your FC continues to hold and you have no CC, assuming your FC matches what it should be for your CYA, you have the correct residual and the algae should not return.

If it were me, under these conditions I wouldn't brush anymore. You've apparantly killed it. Brushing just stirs stuff up. Since you have an easily (hopefully) backwashable sand filter, let the Crud fall to the bottom so you can see what your up against. The water should clear as things settle, then you can vacuum VERY slowly so as not to stir it back up and backwash as needed, getting the Crud out of your pool and filter.
 

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Good point rangeball...I'll just keep up with the vacuuming the next few days. I was worried about my filter functioning before this happened. I'll probably post about that in another thread once everything's clear enough to really reassess this.
N
 
OK...so now my pool is finally perfectly clear :whoot: So...onto the next step...how can I get it sparkling? Hmmm...I just got home from being at the cottage for a couple of days...I think my pool and I just needed some time apart from one another...I developed a horrible case of water chemistry OCD. So...I'll run down right now and get some numbers for you all since I'm sure that will be the first response back to me on this one.
I'm all ready to work on sparkling when you are.
Thanks,
N
 
You are doing great! From this point sparkling water requires attention to the FC level, don't let it get that low again, and time for the filter to clear the fine particles. Other than that the only thing I notice is that if the PH goes up at all from there bring it back down with acid.
 
I can't remember if we discussed it already, but adding DE to your sand filter may help it filter out finer particulates that can leave your water sparkling.

Also, keeping at the upper end of the FC range for your CYA seems to make a difference in my sparkle as well.

Great job!

:)
 
Thank you...yes you did tell me to add the DE and that seemed to be the secret to getting it clear. The water cleared up in no time.
The low chlorine is just due to a couple of days at the cottage. I had to use my best guess at how much chlorine to put in before we left in order for it to be swimable for a get-together we're having this evening. I cut it close...but managed to get the chlorine back up there before people arrived.
I'm going to check the pH again tomorrow and see where it stands.
Clear is fantastic...can't wait to see sparkling :)
Thanks again!

N
 
Funny thread....reminds me of the day I left the Pool Stealer in tears because of their "helpful information" that was completely wrong.....the day I discovered TFP!!!

LOL - We will all be wearing "Scarlet Letters" when we enter the pool store - BBB!!!!!
 
This interesting thread reinforces a lesson that we all sooner or later realize. Pool store testing can be good and it can frequently be very bad. From what I've read of other's experiences, it seems to be more bad than good.
Click to expand...

My pool store told me to add CYA at the beginning of the summer, and then subsequently kept telling me that my CYA was 150. I ended up draining half my pool to get rid of it. The store then tested my CYA at 150 again, and again, and over two weeks, testing every day, it went to 130 and finally 90 before I got Dave's test kit.

According to the drop test in Dave's kit, my CYA was somewhere around 10-20. How could that be? Pool store's mechanized test is 90 - 150. Dave's drop test is 10-20. After emailing Dave, he called me, and together we reasoned that the drop test probably was right. I've added 8 lbs of CYA, and it now registers at around 35-40. Thank you Dave for your test kit!

DO NOT TRUST YOUR POOL STORE TESTS (unless you visit Waterbear).

I could repeat a similar story as the above with regard to salt, because the kid's behind the counter couldn't read the test strip correctly. They just kept telling me to add salt. When I got some strips from Dave and did it myself, I found that I had too much salt!
 

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