Use of Chlorine for shock; high CYA level

Vinyl lined in-ground pool - 16,000 gals. - chlorine filter with trichlor tabs.

The pool has become somewhat cloudy in the past 2-3 days and some early signs of algae this morning. When I tested it with new Taylor kit on Saturday (if I did it all correctly): TA 140, Chlorine tested at 3.5, ph at 7.4, and CYA was high -- at least 100.

Results of pool store analysis today: Chlorine 0, ph 7.6, TA 90, stabilizer 100; I was told to add 8.5 # alkalinity (I prefer baking soda to the pool store product); 12 oz. of algaecide (pool store: 51% copper ethanolamine complex); 4 bags of shock (their suggested sodium diclor) and let pump run overnight. Tomorrow - clean filter and add another 2 bags of shock. They also suggested adding something to increase calcium hardness after the pool is clear, which I question, since it's a vinyl pool.

I'm in Florida, pool is in direct sunlight without enclosure, and temps are in 90s. I prefer not using pool store chemicals and sticking as close to BBB method as possible. Suggestions?

Can I use household bleach (unscented chlorine) for shock or should I use pool store suggestion. Is CYA too high and how do I lower it?

Wow! They didn't give you ONE SINGLE bit of correct advice!

Your problem is very simple.

With your CYA (stabilizer) of 100, you need to get your chlorine level to 25 and not raise your stabilizer any more. Dichlor powder and Tri-chlor tablets WILL raise--so Sodium Dichlor is wrong, whether it's called "shock" or not.

There is NO reason to raise a TA of 90, so adding baking soda is wrong. But, when YOU tested it was 140...you would NEVER raise a TA of 140, though in a vinyl pool, it's not a problem.

Since your pH is 7.6, there's no reason to suspect your TA=90 or 140 to be a problem. Again, wrong.

Calcium is USELESS in a vinyl pool. Its job is to prevent the leaching of calcium out of concrete, plaster and tile pools. So that is wrong.

Copper algaecide and ammonia algaecide are generally worse that useless, staining and creating foaming. So that is wrong.

The ONLY algaecide we recommend is Polyquat 60%, whatever the brand. If you see only one ingredient, Poly...something 60%, that's the stuff. But it's more a prevention than a cure.
What you need to do it pretty basic and will take some effort.

Your are going to need to add lots of bleach or liquid chlorine (same stuff, only stronger) to get your FC to 25. Each gallon of ultra bleach, 8.25% will add about 5.2ppm of chlorine, so you'll need at least 4 gallons to start.
Check your FC 2 to 3x/day and add bleach as needed to get it back up to 25.
Meanwhile, run your filter 24/7 and backwash when the pressure goes up 5#.
Vacuum to waste once a day.
Brush the pool once a day.

When the pool is finally clear, you'll need to maintain the FC level between 8 and 15ppm as long as the CYA is 100 or more. That's OK. You'll probably find you don't need to add bleach too often once it's setlled.

Good luck!

Thanks so much. No more trips to the pool store for me. One other question...my pool chlorinator (part of the filtration system...I guess it's called in-line?) now has trichlor tabs in it. Should I switch to something else since CYA is high?

How many trichlor tabs do you have left? Are they wrapped or unwrapped?

Log out and go to the Pool Chemicals and Pool Water Problems section of the forum. There is a stickied thread at the top that talks about what to do with leftover chemicals. Scroll down and read the section on trichlor.