Algae, Chlorine Levels and Bleach

[cathy]

Yep, my pool was opened a few days ago and it's a lovely shade of green. :-)

This is the first year I've had a test kit showing TC and I was confused by the numbers. My FC is .5 and my TC is 5. Do I add bleach based onthe FC or the TC?

Other info - vinyl, paper cartridge, 22.5K gal; CYA = 100, FC = .5, TC = 5, pH = 7.8, Alk = 140, Hard = 180

[madwil]

The FC- TC = FC + CC, so you have 4.5 CC, which is bad- the FC will gradually eat the algae and oxydize the CC, that's why you need to keep at it!

[aylad]

To clarify madwil's post....
TC = FC + CC. FC is the chlorine available to clean your water, the CC is chlorine that's already engaged in battle. Add bleach based on your FC. With a CYA of 100, you need to get FC to 25 and hold it there.

Janet

[cathy]

I'm having trouble locating that calculator that shows how I convert that into gallons of bleach - can you post that link?

Also, how long after adding bleach should I wait before I retest to see if I need more?

Really appreciate your help!

[cathy]

Now that I've spent more time reading posts, I'm afraid I have more questions...

Since I have a vinyl pool and 25 could potentially take some color out of my liner, should I be trying to lower my CYA first? Is there a way to do that?

Also, if I shocked the pool at 20, would it still work and just take longer? or would I just be wasting bleach?

The site is great - I am learning... Thanks!

[madwil]

the shock levels, based on your CYA levels, will not bleach your liner- 25 ppm chlorine without CYA would be bad for the vinyl liner, but with your level of CYA is not bad as the CYA has it locked in place and limits its reactivity (more or less- chem geek can give precise scientific details)
the level of 20, while maybe not completely ineffective, would prolong your efforts and ultimately be "wasting" bleach- it will take you longer and more effort/money/bleach than if you achieve the suggested levels (and it could be completely ineffective- each pool and situation is unique)
The only way to get rid of excessive CYA is to partially drain and refill your pool- the CYA doesn't react with anything to disappear and under normal circumstances just stays in the pool!
You might, at your level, consider a partial water replacement- 100 is the max level most CYA tests show; your water could be 100, or could be 200 and only shows 100 on the test. Even if your water is truly 100, not higher, the amount of bleach required gets frustratingly high with those CYA levels.
The formula for bleach is simple- whatever % bleach is the ppm per 10k gallons; 6% bleach will give you 6ppm in 10k, 3ppm in 20k, etc...

[CarlD]

You CAN lower your CYA by dilution--drain half your pool and refill and your CYA will probably be 50, rather than 100.

But, as for fading your pool, it won't happen when you shock to 25, because your CYA is 100. CYA=Stabilizer works by actually inhibiting Chlorine's action. So, to protect your chlorine for breaking down from UV rays, we add stabilizer. But that means we need higher initial, shock and maintenance levels to get the same effect. It's a two-edged sword.

The correct shocking level for CYA of 100 or more is 25ppm.

[Furbabyvet]

Did you find http://www.poolcalculator.com ? That's what I use to adjust my chemicals. There is also an app for the iPhone!

[Watermom]

In a 22.5K pool, each quart of 6% bleach will add approximately 0.7ppm of chlorine.

[CarlD]

If you cannot find the calculator, the rule of thumb is:
1 gallon of bleach will add the same number of its concentration to 10,000 gallons. IOW, 1 gallon of 6% adds 6ppm to 10,000 gallons. 1 gallon of 12.5% adds 12.5ppm to 10,000 gallons. So for 20,000 gallons you need twice as much.

The underlying formula used in all bleach calculators is:
(1,000,000/Pool Vol in Gallons) * (Bleach Concentration) * (# of gallons of bleach) = FC added in PPM.

Bleach concentration is a decimal, so 6% is 0.06. 5.25% is 0.0525, 12.5% is 0.125.

For people who measure their pool in liters and buy bleach in liters, simply replace liters wherever I have gallons.

Carl