1st Test with TF100 kit- What went wrong?

[DHinNC]

OK received the new test kit today that I ordered just this past weekend and couldn't wait to see the results.

but not sure what to think of the numbers that I found. Actually removed the winter mesh cover on this past Saturday. Water was super clear. Only a small amount of debris on the pool bottom. Ran the pump at least 6 hours a day while the pool was covered since last October. SWG was set fairly low around 10% over that time. !5K gallon vinyl inground pool figure 8 pool.

Now the numbers

FC <.5 (actually couldn't read any)
pH 7.8
T/A 80
CH 180
CYA <20 (actually no reading could be obtained)
Temp 71 degrees F

Have I done something wrong in the CYA testing? Last spring my local pool supply store charged me $10 to test the water and sold me $45.00 worth of chemicals that I really didn't think I needed. Pool last spring was also clear when I opened it for the season. Never had any problems with algae or other water problems.

Any suggestions on what I need to raise CYA or other parameters besides raising FC number?

THanks in advance!

 

[duraleigh]

DH,

I doubt anything went wrong. It appears you've done the tests correctly and your numbers are not surprising. The big issue is you apparently have no CYA. It is not uncommon for CYA to disappear over the winter in a neglected pool but your pool certainly wasn't neglected. Did you have CYA in the pool when you closed last year? My guess is probably not.

Anyway, that's all water under the bridge. Use Jasonlion's calculator and add enough CYA to bring your pool up to 60-80ppm. Next, I'd add enough bleach to get your FC up to around 6-8ppm....this is simply to help your SWG with the intial dose. The CYA will take a few days to start protecting the chlorine and then you can turn your SWG up until you're able to hold around 4-6ppm daily in the pool. Speculating, that may be around 20-30% but you'll just have to experiment.

 

[DHinNC]

Thanks Dave for the quick reply! I guess last years chemistry was all over the board and we were lucky to maintain good water clarity!

Using the recommeded calculator it indicates that I need to add 10 lbs of stabilizer to bring it up from zero to 80 ppm CYA. And 1-1/2 gallons bleach to get the FC up to 8ppm.

Should I assume that there is actually no CYA present? Or should I be somewhat conservative until I get the reading up where it registers with the test kit?

Also, is it necesary to get FC up before I add the stabilizer or add both at the same time?

 

[duraleigh]

Add the CYA first....it'll get started protecting the chlorine sooner.

It's easy to add CYA but terribly troublesome to remove it so I would calculate enough for say around 50 or so and then bring it up to around 70 a week later.

Add the chlorine in the evening after the sun is off the pool....that'll keep the sun from burning it off for a little while. I was a little hasty with my advice earlier. I would suggest adding enough each evening to bring it up to say 3-4ppm. It'll be effective overnite and then the sun will kill it each day until the CYA starts to be effective....normally in a couple of days but it could take as much as a week for the CYA to be fully dissolved and effective.

Your calcs sound good....so maybe 8 lbs of stabilizer initially and a small jug of bleach each night for just a couple of nights. Then, I think I'd turn on the SWG somewhere around 30% and start measuring the FC each evening....targeting 4-6ppm as a maintenance level.

 

[Guest]

The only thing I would add to Dave's excellent advice is to drop you pH a bit. Turning up the SWG output will have a tendancy to make the pH and you are already at the top of the comfort zone. For a 15K pool you will most likely need around 1 1/2 pints to achieve this. Start with a pint and then test. if the pH is still a bit high add another half pint.

 

[DHinNC]

Ok added 4 lbs of stabilizer yesterday and 2- 96oz jugs of bleach after the sun was off the pool.
Test results today reveal:
CL 5 ppm
pH 7.2
CYA ~20

Looks like the added stabilizer dropped the ph from 7.8 to 7.2 is that normal? Also, the chlorine didn't completely burn off through the day. I'll add more stabilizer starting tomorrow to slowly get the CYA level up to ~60 ppm.

Thanks for all the help.

PS - Water is still crystal clear as long as I keep the Poplar tree blooms skimmed out!

 

[JasonLion]

Keep in mind that CYA can take up to a week to fully dissolve (unless you used the liquid stabilizer). You don't want to add too much so it is better to wait a week after adding some before testing CYA again.

 

[chem geek]

Not only is it normal for the pH to drop when Cyanuric Acid (CYA) is added, but in your case it calculates almost perfectly! With your initial measurement numbers, adding 4 pounds of CYA to 15,000 gallons would lower the pH from 7.8 to 7.17 while the bleach (assuming 6% bleach) would raise the pH from the 7.17 to 7.30 -- so 7.2 is very close. The CYA should have risen to about 32 ppm, but that's not that far off from your measurement of 20 and some CYA will initially stick to pool surfaces. The Free Chlorine (FC) should have risen to 6.2 ppm so you are right that only some of it burned off from sunlight so even the relatively low CYA level is protecting it.

[EDIT] See Jason's post above -- though it appears from the numbers that much of the CYA dissolved, some of it may not as of yet. How did you add the CYA to the water? Did you put it in a sock or panty hose and hang it over a return flow? [END-EDIT]

Richard

 

[DHinNC]

I added the granular stabilizer to the pool with one of the wifes old knee high stockings in each of the 2 skimmers. Wouldn't this method result in the acid be completely dissolved once the stockings were empty or could it come out of solution in the DE filter?

You guys really do add a valuable resource to this website and I would offer my appreciation for all the help that you provide to those of us that feel totally helpless around adult chemistry sets.

 

[JasonLion]

There have been sporadic reports of CYA continuing to rise for a couple of days after it vanishes from a sock but no one has done through testing that I know of. I figure it is better to be safe than sorry.