High CYA, should I drain and re add water?

[LyndonC]

Hello. I have just opened my pool for the first time (purchased home with existing pool)

I have had water circulating for 48 hours and done 2 water tests using Taylor 2006c with nearly identical results so pretty sure it's all accurate.

After all the reading I've done I expected levels to be low and would just use pool math to adjust it up... Didn't account for it starting to high.

Here are the numbers. Since high CYA requires higher FC, is it possible these levels are fine and hopefully CYA drops if only use liquid chlorine (previous owner used trichlor tabs)

FC : 9
CYA : 140? See Attachment.
PH : 7.1
TA : 130
CH : 150

I'd rather not drain and re add water if possible.

Thanks for any suggestions or help.

What is the actual impact on water if both CYA and FC are high but "balanced"? Is it harder on skin?

 

[Donldson]

First thing is you'll want a more accurate guess at your CYA level as that could easily be 200 ppm. You'll want to make a sample of half pool water and half tap water and then use that to run the test again. There's no CYA in tap water so this will effectively halve your CYA in the sample. If you get a reading of 100 or less you'll double it and that's roughly your CYA. If it is still over 100 then you're in for some work...

As for maintaining a pool with CYA that high, it is technically possible but realistically you don't want to do it. If your CYA were 140 (just for example) then you'd need to maintain your FC around 15-20 ppm. At that level your pH readings won't be accurate and you'll need to get more FAS-DPD reagents quickly because you'll be using quite a bit. It would be perfectly swimmable though, but it's just not worth the trouble. I don't even want to think about the 56 ppm FC level you'd need to maintain to clear a green or cloudy pool...

So see if you can get a reading on your actual CYA and we'll go from there.

 

[LyndonC]

Thanks for the quick reply I'll do the half and half mix and re test shortly. Thankfully it's only a 6900 gallon pool so if I need to drain some I'll survive.

 

[LyndonC]

So I finally had a chance to do a second diluted CYA test and the reading made it to 70 maybe 80 which means cya is 140-160.

I assume the best solution here is to drain, sorry I am not really sure on how much to drain though to get a maintainable CYA / FC level. Should I aim for 60/70? That must be about 60% of the water I assume.

 

[mknauss]

What type of pool do you have? This will help us help you on guidance for replacing some of the water to reduce CYA.

 

[LyndonC]

It's 13x20 above ground (6900 gal) with a vinyl liner I do believe. Sorry not sure on make and model.

 

[mknauss]

An above ground pool cannot be completely drained as the liner will shift.

You can drain it down to 1/2 to 1/3 full and then refill. If that does not lower your CYA enough, then you do it again.

 

[LyndonC]

Sounds good.

I realized the pool was around half when I filled it. That must mean they total CYA before it was last drained must have been insane, like 400.... I guess 3-4 years of only using trichlor tabs will get you there....

2 pumps draining water now. Will refill after it passes half way mark.