Cannot maintain FC levels w/ BBB

All,

I have officially switched to the BBB method and turned off my auto-chlorinator! Due to my use of Chlorine Tabs my CYA reading is ~ 90. My other numbers are as follows; PH 7.6, TA 80. My pool is ~ 17,500 gallons and is an above ground vinyl liner using a sand filter. The water temp has been around 76 over the last couple of weeks.

Based on the high CYA I understand that I must keep my FC high (7 to 12 ppm range), but I am having difficulty maintaining this level w/o adding what equates to a gallon of bleach (6.0% or 8.25%) per day. As an example, at 6pm the other day my FC was at 4.6 so I added (2) 121oz jugs of 6% bleach. By 6:40 am the next morning my FC was 10.6 (expected), and by the next morning it was at 6.6 (not expected). So it lost 4ppm of FC in 24 hours. Is this typical? I like the thought of using the bleach, but this could get expensive if I am adding a 121oz bottle of 8.25% bleach (~ 4.5ppm raise in FC of my size pool) everyday.

At the end if the season (3 more months in the NE) I was going to wither drain / refill to lower the CYA or let it sit over the winter to see if the CYA reduces on its own. Is it easier to "maintain" FC with a lower CYA?

Please let me know if I am doing something wrong here. Thanks!

Usually chlorine consumption goes down with high CYA. I wonder if you don't have an algae bloom trying to start. Do you have the K-2006? Do you have a CC level?

The overnight test is definitive for chlorine demand. Measure FC and CC in the evening close to sunset. Repeat the FC and CC tests the next morning close to sunrise. If you have CC or you lose more than 1 ppm FC overnight, there's something in the pool being oxidised.

You may be fighting something in the water which is consuming your chlorine.

In your pool, each of those 121-oz jugs will add about 4.5ppm of chlorine. So, if you had 4.6 in there and added 9ppm more, that would put you at 13.6. But, then you report that by 6:40 a.m. the next morning, you were down to 10.6. That is a loss of 3ppm overnight. When you lose more than 1ppm of chlorine overnight, it is a sign that you are fighting something.

What I am going to suggest is that you go ahead and shock the pool up to 20ppm this evening. Then, a couple of hours after you add the bleach, test the FC and the CC (I assume you have a Taylor K2006 kit?) again and make note of the readings. Tomorrow morning, within one hour of sunrise, test FC and CC again and see how much chlorine you lost overnight.

You need to continue to keep your chlorine at shock level until you can go from sundown to sunup without losing more than 1ppm of chlorine AND you have no greater than 0.5ppm of CC.

Let us know in the morning the results of your overnight test.

Thanks Big Dave.

There is a bit of green spotting on the liner so that could be it.

Yes we have the K-2006 kit and I will have my wife check for CC tonight. I know that it should be at 0, but what should I do if it is higher? Shock the pool?

Thanks again!

Dave and I were apparently posting at the same time, but you see that the advice is the same.

Also, brush the pool while the chlorine is high and run the pump 24/7 while you are working on this.

Thank you Watermom.

We are going to a baseball game tonight, but I will have my wife shock the pool and we will test late tonight.

Thank you all!

BTW, can my daughter swim if the pool is at 20 FC?

With a CYA of 90, sure. Wear an old suit.

Yes, but she will probably want to wear on old swimsuit that she won't care if it fades some.