Can't hold FC

[nepsa]

I opened my pool two weeks ago and my water is very clear, however, I can not get my FC to remain after shocking it about 10 times. My pool store told me to use 8 lbs. to shock that I had a chlorine block. I did so at 6PM that night, however the next morning, I had no FC.
I have an inground pool with 30, 000 gals. My Cyanuric acids are high so I stopped using and products with stabilizers two season ago. I am using a product called Poollife/Calcium Hypocholrite. The odd thing is I had a higher level of CYA last year and had no problem in maintaining FC levels. Listed below are my last test by the pool store. Their suggestion is to keep shocking , but after about 50 lbs of shock, I am not sure that will correct the problem. I did get some 6% liquid chlorine but I have no idea how much to use to shock .

FC .04
TC 1.69
CC 1.65
Tot Alkalinty (Adjusted) 81
pH 7.4
calcium hardness 484
CYA 94
copper 0
iron 0
tot disolved solids 1900
sat. index 0.1

[PoolDoc]

. . . use 8 lbs. to shock that I had a chlorine block. I did so at 6PM that night, however the next morning, I had no FC.

. . . . The odd thing is I had a higher level of CYA last year and had no problem in maintaining FC levels.

Nothing odd about it.

I'm guessing your pool opened 'slimey' -- maybe not green, but with slimey sides?

Regardless what has almost certainly happened is that much of your missing CYA is now ammonia. When you add chlorine, it combines with the ammonia and forms chloramines, including monochloramine. The mono-c is the reason your pool is so clear -- mono-c is what you get when you use Yellow OUT or Green to Clean. But once you get the CC's and add more chlorine, you then oxidized the CCs to salt + nitrogen gas.

There are three options:
#1 - Buy a lot of bleach, and add X gallons each evening, till you stop loosing chlorine overnight, and have CCs of 1 ppm or less.
#2 - Buy an ammonia test kit (or strips), see how much ammonia you have and THEN do either #1 above or #3 below. You may be able to buy ammonia strips at a pet store in the aquarium section.
#3 - Drain and refill. (Of course, you usually can't drain a IG liner pool safely; draining AG pools can be risky, but draining concrete pools is usually a problem only when the pool is in low wet ground.)

[nepsa]

On option number one, any suggestions on the amount of bleach I should add. I read that 1 gal of 6% would raise my ppm by 2. If that is true with 30,000 gal. how high should I shock it? I like the first option as a start. I will get the test strips to test the ammonia.

[PoolDoc]

+ 2 gallons of 6% bleach will add 2 ppm of chlorine to a 30,000 gallon pool.
+ Given your situation, I would start with a 10 gallon dose each evening. If your chlorine levels (OTO after 1 minute) the following evening is 3 ppm or less, repeat. If it's more than 3 ppm, use 5 gallons. If it's orange in color, skip it.

Ben

[nepsa]

Thanks, I will start tonight. I did get an ammonia test kit. The reading was .50 ppm. What reading do i want to get to?
Also, I have ordered a Taylor test kit, but it will not be here until July 15th.

[PoolDoc]

Once you get to a zero ammonia level, you will likely no longer lose chlorine overnight.

By the way, many strips are not very accurate. You might want to test your tap water -- which should be zero ammonia -- just to make sure the strips you got can actually tell the difference between 0.0 and 0.5 ppm.

But, otherwise, the instructions I gave you earlier still hold.

Ben