3 partial drains, cya still 100??!

[Hlynnkirk]

Hi all! New to tfp, just got my test kit on Tuesday. We have done three partial drain and refills, approximately 30 to 40% of the water each time. All this since Tuesday. While my cya does seem to be trending down from somewhere well above 150 to approximately 120, and nowafter the third drain and refill it is still reading at 100 on a diluted test. Water is really expensive here, so an additional drain is out of the question. We have more or less replaced our entire pool at this point. What now??

FC 21
CC 0
pH 8.0
Alk 130?? (Sample went orange but would not go red)
CH 140
CYA 100?

I should add that we are heading out of town for the weekend, and chlorine is high from an algae prob prior to joining TFP. We've also got metal stains returning ? HELP!

 

[Texas Splash]

Oh, that stinks. That is perhaps the downside of partial drains - mixing old concentrated CYA water with new water. Then you go to drain the next time but now it's still relatively high from mixing the incredibly high (old) CYA water with the new. No doubt you must get the CYA down before you can SLAM or do anything else. Since you know you have metal (I'm assuming iron, maybe from a well?), is there any chance you can have fresh water trucked in? That would kill two birds with one stone - CYA & iron.

 

[borjis]

Something definitely seems off.

My first home had a 20,000 gallon pool with CYA diluted test showing 300+

Draining down to the top of the light ring and refilling 2 times, got the cya down to 80. (undiluted cya test)

Water in that area was really expensive too, my water bill was $ 480 that month.

So it stayed at 80 until I sold the place a year later.


How are you doing the CYA test?

It's vital to do so on a clear sunny day, back to sun, holding the test tube at waist height then
putting in the cya/water mix to the 100 mark. look at the dot, then look away, look at the dot, then look away.
Add more to the next cya number on the tube if you still see the dot. repeat as necessary until you don't see the dot.

The water sample should be around 70 degrees/room temp (higher is fine too, just not 60 or lower degrees as that can read low)

 

[Hlynnkirk]

We have a vinyl liner, so fully replacing the water is not an option. My pool guy says I can safely drain down to the top of the Second Step, which is what I have now done three times. Perhaps I'm just not doing the diluted test correctly, but I've more used all the initial cya regent and more won't be here till Tuesday.

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We're on City water, btw

 

[jblizzle]

Assuming your CYA testing is corrent ...

Sorry, you really should replace more water.
It appears that you did not get a very good estimate of the CYA level before you started replacing water.

If you are only replace 1/3 at a time, you will only lower the CYA that much each time.
If started at say 300pmm, after replace 1/3 of the water you would be at 200ppm
then another 1/3 would lower it to 134ppm
then another 1/3 would lower it to 90ppm

Had you done 1/2 replacement (perhaps not possible with your liner)
From 300 it would have dropped to 150
from 150 ir would have dropped to 75ppm

In both cases you would have put your entire volume of water into the pool, but the end CYA level is different (and still not 0 of course).


Options are:
1. Do another water replacement. Follow the SLAM Process process at a lower CYA or ~65ppm if you are at 100 and replace 1/3 (shock FC level of 26ppm). Then deal with stains. And then keep FC above 5ppm at all times.

2. Follow the SLAM Process process at your high CYA assumine 100ppm (shock FC level of 39ppm) = a lot more testing drops. Then deal with stains. And then keep the FC above 8ppm at times (remember that pH test is not valid when FC > 10ppm, which you will often be).

Note that currently your FC is not anywhere close to the required shock level for your high CYA.

 

[Hlynnkirk]

We've had tricky weather this week.. Lots of clouds and rain. I did the test at 730 tonight, so sun was going down, but otherwise followed instructions to the letter. Maybe I just need to wait and try when sun is fully out?

 

[kellyfair]

Yes, try to test when sun is out

 

[borjis]

The lighting conditions do make a significant difference i have found.

I was testing at first inside under a lamp and it read incorrectly than actually was.

how are you calculating the dilution? That too might be a reason.

 

[Hlynnkirk]

I guess I'm also wondering if I need to do a slam? Combined chlorine is at zero, pool is clear and blue. Can I go ahead and let the FC drift down to 8? Adjust pH and TA once it's there?

 

[jblizzle]

If the water is crystal clear and no sign of algae, then do the Overnight Chlorine Loss Test and see if you need to follow the SLAM.

 

[Hlynnkirk]

I guess I'm also wondering if I need to do a slam? Combined chlorine is at zero, pool is clear and blue. Can I go ahead and let the FC drift down to 8? Adjust pH and TA once it's there?

Was testing inside under halogen lighting yesterday. Tonight was outside in (fading) sun.

As far as test goes, 7 ml pool water mixed with 7 of tap. Shake, pour off 7, add 7 of cya regent. Read.

 

[proavia]

You reported your FC at 21. Did you use liquid chlorine, granular schock or something else to get it to that level?

 

[jblizzle]

And it is not "down to 8" it is keep above 8 at all times. Likely you need to add chlorine up to 11ppm or so every day so that it does not drift down below 8 before the next day you test and add.

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That is the correct dilluted CYA test process ... other than not using the correct lighting conditions when you read it.

 

[Hlynnkirk]

Concentrated bleach. 10%

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Got it. Ok. Whelp, looks like we'll try the test again when my replacement regent arrives and keep the FC above 8 until I can confirm. Will do the chlorine loss test tonight. Thank so much y'all! The help here had been outstanding despite my pool frustrations !

 

[proavia]

Concentrated bleach. 10%

Just double-checking it wasn't something that was adding CYA in. And of course, liquid doesn't.