Large Pool Problem

[JonKneeV]

Hi all,

My wife and I moved into our new home on 3/1/2013. Our house came with this wonderful 45,400 (!) gallon pool.

In the last week, our pool has been a nightmare even though we bring in a water sample to our local pool store each week.

6 days ago we came home to cloudy, slightly green pool. We were told to shock the pool and come back the next day with another sample to Pools of Fun. The shock had not fixed the problem. They did some research and we were told that the previous owners had never changed the sand in the filter (6 years). We proceeded to do that. In addition to changing the sand, we were advised to do a drain and fill taking the pool down a foot.

The drain and fill did nothing and we were notified that we have 8 ppm of ammonia. The pool store advised that the ammonia is too bad to treat so we should do another drain and fill.

This time we drained 2.5-3 feet of water. The ammonia is still at 8 ppm. During the drain and fill process, we were told to keep the chlorinator off as the chlorine is part of the problem with the cloudiness.

So here we are. The following test was done today by Pools of Fun:

CYA: Not tested

TC: 1.1

FC: 0

pH: 8.1

TA: 290

No Algae

Test from Leslie's Pool Supplies:

CYA: 10

TC: 2

FC: 2

pH: 7.6

TA: 220

Leslie's said they do not test for ammonia, but they said if we use granular shock and Muriatic acid the pool will be back in balance.

Please help. I'm so confused and we've already used about 20,000 gallons of water.

[chem geek]

It sounds like the FC level got to zero and bacteria grew in the pool converting the Cyanuric Acid (CYA) into ammonia. That creates a huge chlorine demand, but if your ammonia level is truly only 8, then that's around 80 ppm FC cumulatively added to get rid of it. If I were you, I'd take a 2 gallon bucket of pool water and see how much chlorine bleach it takes to add to it before the FC level holds reasonably well. 1/4 teaspoon of 6% bleach (about 1/5th teaspoon of 8.25% bleach) in 2 gallons is 10 ppm FC. If it doesn't take an extraordinary amount of chlorine, then you could add chlorine to the pool to get rid of the ammonia. Your only other option is another partial drain/refill to dilute the water more.

To prevent this from happening again, you need to maintain a proper chlorine level in your pool. After you get rid of the ammonia, you need some CYA in the water to prevent chlorine breakdown from sunlight but you don't want the CYA too high either -- about 50 ppm for a manually dosed pool is usually about right. The FC level has to be no lower than 7.5% of the CYA level at all times so you dose higher than that so that it gets down to no lower than this minimum by your next dose. You need to understand the following facts for what else is added by various chlorine products which is why chlorinating liquid or bleach is preferred since it doesn't add anything you don't want.

For every 10 ppm Free Chlorine (FC) added by Trichlor, it also increases Cyanuric Acid (CYA) by 6 ppm.

For every 10 ppm FC added by Dichlor, it also increases CYA by 9 ppm.

For every 10 ppm FC added by Cal-Hypo, it also increases CYA by at least 7 ppm.