High CYA, drain 1/3 refill?

22K inground plaster pool, test kit indicates CYA higher than 100. Having issues with algae bloom with 8.5ppm free chlorine. Going to drain 1/3 and refill. Been using pucks and liquid chlorine, will stop using pucks.
Sound good?
Fatstogie

Yep, sounds like a plan, just don't drain enough of the water out of the pool to float it, if you have a high water table.

You've been doing your homework--kudos to you!! :)

And, welcome to the forum!!

I am on the side of a hill, no water table. If there was a water table how far below it is safe?
curious

Before you do a partial drain and refill, you might want to figure out just how high your CYA actually is. The limitations of the test will not differentiate readings higher than 100 so a result of 100 might mean 100, or 300 or 500 or ?? If it's super high, then draining a third of the water might not make that much difference.

Dilute the water sample one part pool water and one part distilled water and then run the test again and multiply the result by 2. If you still get a reading of 100, do one part pool water and two parts distilled water and multiply the result by 3, etc.

Do you want to drain 1/3? If you do, I guess that's fine.

But, simply knowing that your CYA is greater than 100 is not a good starting place. If it's 400 ppm currently, and you drain and replace 1/3, it will go down to about 265. If you do the same thing 2 more times, it will go down to about 120, and STILL be over 100, even though you will have added enough water to have done a 100% drain and refill.

How are you testing? If it's with 'guess-strips' -- or a 'guess-strip' reader, you really don't know anything at all. The CYA test is the worst of a bad bunch of tests, on strips, and can be horrendously inaccurate. Probably your FIRST step, if you are primarily concerned with your CYA levels, is to get a reasonably reliable result from a GOOD test kit, using a distilled water dilution.

Get one of THESE kits:

HTH 6-Way Test Kit @ Walmart
Taylor K2006A (3/4 oz bottles) @ Amazon
Taylor K2006C (2 oz bottles) @ Amazon

AND a gallon of distilled water from Walmart (or whatever big box store you like).

Then, collect mix 1 cup of POOL water with 2 cups of DISTILLED water. After stirring, do the CYA test, and multiply the result by 3. The CYA test in these kits is not great either (much better than strips, but still not great!), so looking at the videos here, http://www.poolforum.com/pf2/showthread.php?17157 , may help. The HTH 6-way drops is ALSO a Taylor kit, so the videos still apply somewhat.

Thanks forgot that trick. I will dilute 50% with distilled water measure and repost.

I diluted 2/3rd's remeasured and it reads aproximately 38, so the pool must be around 114. Looks like I need to drain at almost 1/2?

If your target CYA is 60, yes. If it were me, I'd just switch to bleach or cal hypo. But, I don't know what's available to you inexpensively, and I don't know what your calcium levels or equipment set up is. It's hard to use cal hypo long term, if you don't have a sand filter.