CYA - drain and refill - weird results

[jandersen13]

Hey everyone,

I did a partial drain and refill over the last 2 days as my CYA was showing between 100 and 120 with the diluted sample test. I drained and refilled roughly 30%. My goal is to get to 70 or 80 as I’m converting to saltwater next week.

After the refill today I waited 2 hours after the pump was back on to test for CYA again. I did 2 tests and the results are odd:

- first test was diluted and came back pretty clear at 40 and almost could see it to 30.
- second test. Because the diluted was good, I tested regularly and I lost the dot somewhere between 80 and 100.

My question here is, what do I believe? Is my CYA 60 - 80 based on the diluted test? Or 80-100 based on the regular test? And if it is the regular, why would that be?

 

[markayash]

What’s your water temp, if it’s too cold you get high reafings. I did the same and was still reading high until I tested again after I took a bottle inside and let it warm up.

 

[Jimrahbe]

13,

I would trust the regular test...

But, is not a diluted test of 40, the same as a regular test of 80???

Thanks,

Jim R.

 

[jandersen13]

I didn’t let it warm up. I can do that tomorrow. The water temp is 60.

Yes, the diluted test was seen pretty good at 40. I lost it at 30. So was thinking CYA is between 70-80. But the regular test I lost it between 100 and 80. So that showed higher it seems.

I can test again tomorrow. But wondering if I need to drain again as I’m in range for saltwater I think. Thoughts?

 

[Rancho Cost-a-Lotta]

Two hours may not be enough time for the old and new water to mix. I bet you see the expected results in the am. Let the pump run overnight.

 

[mknauss]

The diluted test has more than double the error of the regular test.

 

[jandersen13]

Ok good to know. I will retest it tomorrow morning and do the regular test to see what it shows. Thanks!

 

[jandersen13]

Oh another question. Should I target CYA of 80 for saltwater then? The Chlorine / CYA chart shows 70 or 80 is ideal. Should I shoot for 70 in case there is error, or is 80 ok?

 

[Richard320]

Ok good to know. I will retest it tomorrow morning and do the regular test to see what it shows. Thanks!

Also remember you can go back and forth between mixing bottle and view tube as many times as you need to feel confident.

I've even noticed a difference in readings whether I hold the tube naturally or just at the very top with one finger and thumb.

Update: if you're anywhere near 70 or 80 you're good. Adjust FC to CYA, don;t keep adjusting CYA. You've changed enough water

 

[jandersen13]

Great, thanks @Richard320! I have read on here the benefits of why I should have the CYA that high for SWG and it makes sense. My concern is if I ever need to SLAM. Do people with SWG run into issues there or it being a big pain?

 

[Richard320]

Great, thanks @Richard320! I have read on here the benefits of why I should have the CYA that high for SWG and it makes sense. My concern is if I ever need to SLAM. Do people with SWG run into issues there or it being a big pain?

If the SWG is running, they won't get algae. Many people here have gone years and years without ever seeing a green pool.

If it's green in the spring, they probably drained down for winterizing so the salt and CYA are already reduced.

 

[jandersen13]

Ok good to know, thanks!