Question- TC but no FC

[mccato]

Hi all! I took my water to the pool store for testing this morning. There is TC, but no FC. I used BleachCalc and put 3.6 gallons of bleach in to raise the cl level to 18. Will this take care of the split? Or will I need more bleach to get the FC up? How do I calculate how much? I'm worried about going over 20 because I have a vinyl liner. Oh, and I've added some Lo N Slo to bring the pH down.

Here are the numbers:

In ground, vinyl 16,400 gallons
CYA 75 (this is down from over 400 in Sept!)
TC 5.5
FC 0
pH 8.1
TA 163
TH 159

Thanks so much for your advice!

[mbar]

With a cya of 75, you will need to take your ph up to at least 20 ppms for shock - you need to maintain a minimum of 5ppms at all times. Check the "Best Guess Chart" Sticky. I wouldn't worry about going over 20ppms because of all the cya you have in the water.

First I would add some muriatic acid to take the ph down to 7.2. Then add enough bleach to take your chlorine to 20. When your chlorine is at 20 your ph will not test right - it will test high, so disregard the ph till you get back to regular bleach levels. You will know you have killed whatever is in your water when your free chlorine holds overnight. You should test 3x a day and take it back to 20 each time. Keep the filter running 24/7, and brush the walls of the pool. If you do this and be consistant then you should be holding your chlorine level overnight faster. Once your free chlorine is holding, you can let your chlorine drift back down. Then test ph, and don't let it get over 7.8. You can also take your ph down to 7.2 and turn your return jets up to aerate the water, this will take your alk down and raise your ph back up to 7.4 - 7.6. You can do this because your alk is a little high, it should be between 80 - 125 in a vinyl liner. You don't need calcium in a vl, unless you have a heater - your calcium level is good. Feel free to ask any other questions

[mccato]

Thanks, Marie! You're a wealth of information! I'll get started brushing now!

[aylad]

There is TC, but no FC.
Here are the numbers:

In ground, vinyl 16,400 gallons
CYA 75 (this is down from over 400 in Sept!)
TC 5.5
FC 0
pH 8.1
TA 163
TH 159

Thanks so much for your advice!

Are you sure that the FC was zero, instead of the CC? If you truly had FC of zero and CC of 5.5, which is what your numbers indicate, I would expect to see cloudy, green, really yucky water. What does your water look like?

Janet