High Cya Level

[mglange1]

Problem: Water is starting to turn green. My current CYA level is 100+ . Should I do any water treatment before draining at least 1/2 of the water? From what I've read draining is the only way to bring CYA levels down, is this correct? Before refilling the pool, is there any wall cleaning, water treatement, etc. I should do?

FC: 0
TC: 0.5
pH: 7.2
TA: 132
CH: 200
CYA: 100+

My pool: in-ground, 21,000 gallon, gunite
Pool chemicals: BBB
My pump & filter: Hayward Pro Series filter w/Zeo-Sand & a 2 HP pump
Other info: The fountain is not currently attached to pool system

[chem geek]

You said you were using BBB for pool care, but you wouldn't have the CYA get so high if you were using bleach (or chlorinating liquid) as your source of chlorine, so what happened?

You are going to need to lower the CYA level eventually anyway, so you might as well start on that water replacement now doing partial drain/refill (perhaps multiple times, depending on how much you can drain -- usually only a foot or so at a time depending on your water table). Have you read Turning Your Green Swamp Back Into a Sparkling Oasis?

[czechmate]

100+ CYA. Did one last year that was at the top of the color chart. Drained almost all except 3ft in the deep. Should have done more, since after fill that followed immediately and took till morning the CYA was still 45.
Which means maintaining FC of around 5ppm. Would have been much happier with CYA of 35-40, which was only 1 hour of more draining. Water is cheap. Maybe 50-60 bucks to fill whole thing.
Keeping FC 5ppm is not cheap.
If the ground is not saturated with recent rain, it should be safe to drain all but 2 1/2 ft in deep. The weight of concrete, plus the extra drag of rough concrete on the surrounding soil (backhoe print) is save in normal soil moisture. It is very helpful if you pressure wash the algae of the exposed walls as the water level goes down.
It goes out to P-trap directly and will not clog up your filter later. Buy a 60.00 auxiliary pump, 4 sticks of schedule 40 to fit it, few fittings and you go to town. Drains a lot faster than it fills. Fill with 2 hoses, always.
You watch time and calculate the rise. That way you may leave one hose filling overnight and adjust the faucet. That will eliminate any rings on plaster. Remember, as the surface gets bigger it takes more time to gain inches. That is also your calculating cushion against overflow. Or set up an alarm clock if you not sure.
Good luck!

[mglange1]

Czechmate,
Thanks for your input, you verified the steps I was going to take. I'll drain it empty to make sure the CYA level is as low as possible after refilling. I have a power-washer and will clean the walls before refilling.
ChemGeek,
I didn't start using BBB method until late last fall. Brief history, I bought the house late 2007. The pool was a mess, spring 2008 I cleaned it out, fixed a couple leaks in the return pipes and put a fresh coat of white paint on. I used Leslie's products that first year and all went very well. Pool stayed clean all season with little cost in products. Pool looked good until early May 2009. I had web-worms in the pecan trees around the pool. I had tons of little black pellets in the pool on a daily basis (web-worm poo I think). All the surfaces in the pool started getting stained a yellowish-beige color. Stain & Scale Remover from Leslie's would clean things up and it would look good for about a month. I noticed the amount of chlorine I was using rising. As the weather got hotter this cycle repeated itself over n over. By the end of the summer, the Stain & Scale Remover would only work for a couple weeks. I treated the pool 5 times with the Stain & Scale Remover. I was using 10-15 lbs of chlorine a week and still having problems keeping water from turning green. Do you think the Stain & Scale Remover & web-worm poo led to the CYA levels getting so high? I found this website in the fall and after reading many articles understood why I was using SO much chlorine. I was very disappointed in the help I received from Leslie's. I was in there on a weekly basis toward the end, for water tests, answers to why I was using so much chlorine compared to the year before and advice on what I needed to do. CYA levels was only briefly mentioned but never how high levels of this effected the amount of chlorine needed. After finding the Pool Forum and reading about BBB I decided to take matters into my own hands.
I drained 3/4 of the pool and refilled it late last fall. I bought one of the test kits (TF-100) I seen in the articles. Even after this the CYA levels were still 100+. Not sure how high it was before draining. It still tests 100+, however it was slightly lower than last fall. The CYA test tube only gives a reading of 100 or less, and the black dot disappeared before reaching the 100 level. I repeated the test twice both times to verify the results.
You mention only doing partial drains/refills, is this better way of doing it? My plans are to drain it all and refill it this coming weekend. OK my brief history isn't so brief anymore, thanks again for both of you.

[chem geek]

A complete drain can be dangerous and pop out or crack the pool if the water table is too high, hence the advice about partial drain/refill.

The stain & scale remover can increase chlorine demand, especially if it's EDTA. The best ones use HEDP that doesn't increase chlorine demand and lasts longer.

You said you used pounds of chlorine from Leslie's so that sounds like either Trichlor pucks/tabs or possibly powder/granular or Dichlor powder/granular. The following are chemical factual rules that are independent of concentration of product or volume of pool and should have been disclosed to you:

For every 10 ppm Free Chlorine (FC) added by Trichlor, it also increases Cyanuric Acid (CYA) by 6 ppm.
For every 10 ppm FC added by Dichlor, it also increases CYA by 9 ppm.
For every 10 ppm FC added by Cal-Hypo, it also increases Calcium Hardness (CH) by at least 7 ppm.

You can learn much more about how to properly maintain your pool by reading the Pool School.

Richard