# Thread: chemistry with a drain and refill

1. ## chemistry with a drain and refill

We had a major wrinkle in our vinyl liner over the winter, so we drained the 27,000 gallon pool to about 1/3 of the way down into the diving well. Now that the liner is fixed and the water level is back up (after four straight days with a garden hose), I have tested the water. It has a fair amount of sludge floating around in clear water, so I know I need to get the chlorine in right away. Here is the first set of numbers:

FC <1
pH 7.5
TA 70

The CYA test was hard to figure because the water was above 20 and was just slightly cloudy. I've seen the warnings about being careful if your CYA is truly zero. I don't think it's zero, but I'm not sure what to plug into PoolMath. Suggestions?

I'm going to calculate how much CYA I need using PoolMath and add it in a sock. But do I add chlorine according to the initial CYA level or according to the amount of CYA I add? I know it takes several days for the CYA to fully incorporate into the water.

Here's the next complication...I'm leaving town for a week, in about three days. I'll be doing well to teach my daughter and husband how to test and add chlorine while I'm away. Is it important for them to mess with any other tests/chemicals over the next week, or can everything else wait until I return. No one will be swimming.

Thanks!

2. ## Re: chemistry with a drain and refill

I would add about 20ppm of CYA and assume you are around 30ppm and use that in PoolMath. Then verify the [s]FC[\s] CYA level in a week.

Just get the CYA in dissolving. Lower the pH a bit. And then all they should need to test is the FC and maintain at SLAM level.

And clean the filter when the pressure rises 20-25% over the clean pressure.

3. ## Re: chemistry with a drain and refill

Verify the FC in a week? I was expecting you to say to verify the CYA level in a week.

So once I add the CYA, is it ok to SLAM right away?

I won't have time to complete a SLAM before I leave town, and my husband doesn't have a clue about how to maintain the pool, much less shock it. If they test each evening and bring the chlorine level up to the regular goal level, might I expect that it won't be a frog swamp when I return? Then I can SLAM it when I get back. And teach my family to help take care of the pool.

4. ## Re: chemistry with a drain and refill

Oops, yes verify the CYA after at least a week.

As soon as you add the CYA and lower the pH, you can start SLAMing assuming that the CYA is working. The stabilizer from Wal-Mart gets good reviews and dissolves quickly.

5. ## Re: chemistry with a drain and refill

Thanks so much! I am always amazed by how quick the responses are.

- - - Updated - - -

So I just checked Pool Math, and it says my pH should be 7.5 to 7.8. Why do I need to lower my pH a bit? What am I missing?

6. ## Re: chemistry with a drain and refill

You want the pH lower before you start to SLAM because once the FC is over 10, the pH test is no longer valid. And raising the FC higher with bleach gives a temporary pH rise.

7. ## Re: chemistry with a drain and refill

Cool! I didn't know that. Thanks again!

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