Opening pool with high CYA

matali · May 18, 2015

Hi,
We just opened the pool.
Last year we struggled with high CYA (after buying the house) so we want it make it right this time.

I measured the water (using TF-100) and here are my results:
PH 7.5
CYA 110 (initial reading was more than 100, so later I measured CYA for pool water mixed with tap water which was around 55)
FC = 4
CC = 0.5
CH = 100
TA = 110

We plan to drain at least half the water.
What should we do next? The pool store would like us to drop 6 lb of shock but I want to ask you, the experts.

Thanks in advance,
matali

JasonLion · May 18, 2015

What does the water look like?

As long as you are replacing water very soon, I would focus on the water replacement before worrying too much about anything else.

bdex · May 18, 2015

I agree with Jason. No sense in paying for and putting a bunch of chemicals into the water only to pump out half of them into the drain.

Have you used pool math to determine how much water you need to replace? What is your goal cya number? Your signature is cut off on my phone but are you SWG?

And avoid the pool store at all costs.

Sent from my iPhone using Tapatalk

Isaac-1 · May 18, 2015

Also is that shock they want you to use dichlor, or trichlor, is so it will add even more to your CYA, this is why we suggest only using liquid chlorine / bleach as it does not contain CYA

Swampwoman · May 19, 2015

Welcome, matali. I just want to check to make sure that you know that when you drain a vinyl pool you should leave a foot or so in the shallow end to avoid creating liner issues, so please take care in your draining. Some folks will, for example, do two 30% drains instead.

If you have a high water table, you can also add water as you drain to maintain the pressure on your walls.

But I agree that drain/replace is your best first step. Best wishes!

matali · May 19, 2015

Thank you for all your answers!

The water still looks OK - clear with lots of insects.
We won't have backwash hose till tomorrow so I wonder if I should dump any bleach before draining. What do you think?

Regarding CYA - for what level should I aim? If I replace half of the water I will get around 50-55. Is it still too high? Should we drain maybe 66%, so we'll end up with 40? I checked that the recommended level for Vinyl/Bleach pool is 30-50.
And I haven't done yet the pool math because the shape of the pool is irregular and I need to look at it to make a better estimation.

@ Swampwoman
What do you mean by doing two 30% drains? Is it draining, adding water, and then draining again?
Our shallow part has just 2 ft 10 in, so we'll need to be careful with that.

Thanks again for any advice,
matali

tim5055 · May 19, 2015

I would add some bleach to keep it clear. You don't need it green on top of having high CYA.

The higher the CYA the more chlorine you need both on a daily basis or forbid, the massive amounts you would need to SLAM your pool. With a short shallow end I would go ahead and drain leaving the foot of water in the shallow end, refill and test again. I started at 200+ and was happy when I got below 100 and ecstatic when i got below 60. In a perfect world 50 would be great, but even if you end up a little high you should be able to manage it. Stay on top of your chlorine additions and no solid chlorine!

pooldv · May 19, 2015

Welcome to TFP!

Good job doing a partial drain and refill to lower your CYA level. I would definitely add bleach/liquid chlorine in the meantime to keep the algae away.

After you finish the drain and refill, the most important part is to keep your chlorine level above the minimum level for your CYA level on the Chlorine CYA Chart. Allowing FC to drop below the min will let algae start growing.

Here are some intro Pool School articles to read
TFPC for Beginners
ABC's of Pool Water Chemistry

Here are the Recommended Levels for your pool.
Here are the Recommended Pool Chemicals to maintain your pool and how to add them.
Use PoolMath to figure out how much to add.

Swampwoman · May 20, 2015

^matali, I meant wat Tim clarified...to drain to leaving a foot in the shallow end, fill, retest the cya, then drain again if needed to dilute further. Just don't want you to inadvertently float, shift or harm your liner, which relies on the water pressure to stay where it belongs