1. ## Lower cya

My cya is at 150 ppm what percentage should I drain to lower the Cya.

2. ## Re: Lower cya

Do you know how to use PoolMath?

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Here is a tutorial: Pool School - PoolMath

3. ## Re: Lower cya

Originally Posted by Pete23
My cya is at 150 ppm what percentage should I drain to lower the Cya.
Without knowing what type of pool you have, what your water table is, or your CYA goal I don't see how your question could be answered.

Dom

4. ## Re: Lower cya

It's a concrete pool about 10000 gallons I want to lower it to around 50 -75 ppm.

5. ## Re: Lower cya

You still need to learn how to use PoolMath. Drain 2/3.

6. ## Re: Lower cya

Do you know how high the water table is in your area? Draining a pool below the water table could cause the pool to float & pop up out of the ground.

Dom

7. ## Re: Lower cya

I don't know what the water table is.

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The pool is about 5'5 max depth.

8. ## Re: Lower cya

Call the county.

9. ## Re: Lower cya

Ok. So it can't be lower? Do you think my local pool store will have that info?

10. ## Re: Lower cya

Call the county in the morning.

11. ## Re: Lower cya

What's the number they give me?

12. ## Re: Lower cya

Water table depth in your area. Call and let us know.

13. ## Re: Lower cya

I've spent most of my morning calling around and my county doesn't have a water department so I called the water servicing company in the county and they didn't know, so then I called my city and they tried directing my to the county and finnaly I tried a local pool store and they said to call the city. What else can I do?

14. ## Re: Lower cya

The danger you face when draining a pool too much is that a couple nasty things could happen. The water, which is heavy, and fills up the cavity of the pool, applies pressure to the walls. Too little pressure and the dirt or whatever is outside the pool, pushing back, could cause a cave in. Physics, for every action...

Secondly, too little water in pool could cause your pool liner to become the hull of a boat, and float. The weight of the water is keeping that from happening, like a sunken ship.

They are wanting the water table information to determine a safe distance to drain.

However, if you're not sure, and can't find out, and willing to take on a little risk, you'd probably want to do a few smaller drains of your pool vs. one massive drain. Using the poolmath tab at the top of the page you can put in your pool info and calculate how much CYA you need to drain, which is probably 50% of your pool or more. Adding water back to the top, however, will dilute what's left, and you'll need more than 2x1/4 drains to equal 1/2 of the pool drained. Poolmath is your help there.

To be safe, most guys will tell you if it's an in ground plaster pool to not drain further than the bottom step on the shallow end. So the last step is still submerged slightly. For my pool, and your mileage will certainly vary, that was about a 40% drain.

15. ## Re: Lower cya

Building department? Permits?

16. ## Re: Lower cya

I don't think I'll drain it, I don't believe it's worth the risk.

17. ## Re: Lower cya

There is no way to get the CYA number down if you do not drain the water. CYA stays in the pool for a long time.

Also, CYA is linear, so if you have a 150 level and want to get down to 75, you need to drain exactly half of your water. If you want to be at 50, 2/3 of your water.

To make it easy, drain 1/3 of your water, that won't be enough to cause any floating or other issues, but you will then be at 100 when you refill with water. Again, drain 1/3. Now you will be down to roughly 66. If you can live with that, you are done. If you want to get from 66 to 40, that's going to require another 1/3 drain and refill.

18. ## Re: Lower cya

Do you think draining one end and filling the other end would work effectively?

19. ## Re: Lower cya

New Page 1 I found this graph of my state and it says between 0-15 so I don't believe it's accurate enough.

20. ## Re: Lower cya

By the way, how did you test to get a CYA of 150?

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