Clarification: CYA dropping due to pool closing/winterizing?

[juzzie]

I have noticed that some of the posts regarding pool closing and high CYA levels say that the CYA level will disappear over winter.

Do the CYA levels only drop due to removing the water for a proper winter closing??? And then when you top up the CYA levels are therefore diluted?

I am in southern hemisphere in a colder part of Australia and have extremely high CYA levels - 170.

Swimming season here is only really November --> March and overnight temp doesn't really get below about 5C / 40 F very often. So not necessary to drop any water levels etc.

So I am trying to get on the front foot for opening up in two months time....

Do I have no choice but to drain or is there a chance the CYA levels will drop over the period of 2 months?

TC - 0
FC-0
CYA- 170
pH - 7.7
TA - 195
CH - 242

(Results from local pool shop, and they are telling me to put more trichlor in! Checked some test paperwork from last year and the CYA was 213 and they were still telling me to put trichlor in. That's the reason I am here!)

 

[JohnT]

Re: Clarification: CYA dropping due to pool closing/winteriz

Many people experience significant CYA drop over the winter, probably much more than could be attributed to water exchange. I start every year at 0ppm or close enough to that that I can't measure it. This past winter I never had to drain the pool, and still ended up with no CYA left. It is probably the result of decomposition due to the pool not being sanitized.

That said, don't believe a CYA test result of 170ppm. The test isn't accurate at such high levels. It could be higher or it coud be lower. You can test a 50-50 dilution of pool water and tap water to get a better idea of where you stand. The mixture should test at roughly half your actual CYA level.

 

[juzzie]

Re: Clarification: CYA dropping due to pool closing/winteriz

Maybe some more chemistry trained person out there could comment - maybe if the water gets very cold or even freezes maybe some of the CYA precipitates out of the water?

Absolutely cannot wait until I get a proper test kit!

So you don't add any chlorine at all over winter?

I have been throwing in a bit of calcium hypo every now and then (ie once a week) and also using the trichlor pucks because that is what I was told to do... And running the filter for an hour or 2 weekly.

Now I think I should just leave it alone for a while, at least till I get my test kit.

 

[UnderWaterVanya]

Re: Clarification: CYA dropping due to pool closing/winteriz

Bacteria can consume the CYA with or without ammonia as a byproduct. This seems to account for the zero CYA opening some people have. Drain and fill can reduce CYA but not eliminate it. CYA does not precipitate out.

 

[juzzie]

Re: Clarification: CYA dropping due to pool closing/winteriz

Many people experience significant CYA drop over the winter, probably much more than could be attributed to water exchange. I start every year at 0ppm or close enough to that that I can't measure it. This past winter I never had to drain the pool, and still ended up with no CYA left. It is probably the result of decomposition due to the pool not being sanitized.

That said, don't believe a CYA test result of 170ppm. The test isn't accurate at such high levels. It could be higher or it coud be lower. You can test a 50-50 dilution of pool water and tap water to get a better idea of where you stand. The mixture should test at roughly half your actual CYA level.

OK got my TF100 and did the CYA test as you suggested - 50% pool water and 50% tap water.

And I couldn't see the dot way before the level was even halfway between the bottom and the 100 mark.

So does that mean I am well over 200???

I might try diluting the mixture 1:4 and see how the test goes?

How high can the CYA level go???

 

[duraleigh]

Re: Clarification: CYA dropping due to pool closing/winteriz

As long as you keep putting CYA in the pool, it will continue to accumulate.

The accuracy of the CYA test is worthless in a 4:1 dilution but suffice it to say you have w-a-a-y too much.

Where are you keeping FC?

How does your water look?

I think draining (in steps) that pool is almost mandatory if you want to keep it algae free this coming season.

 

[UnderWaterVanya]

Re: Clarification: CYA dropping due to pool closing/winteriz

The accuracy of the CYA test is worthless in a 4:1 dilution but suffice it to say you have w-a-a-y too much.

Why is that? Or is this a chem 201 question? My assumption is that if someone had 200ppm cya and diluted 4:1 the water sample would have 50ppm and be well within range of the test. Is the problem the accuracy of the dilution?

-sent with Tapatalk 2

 

[yeggim]

Re: Clarification: CYA dropping due to pool closing/winteriz

The accuracy of the CYA test is worthless in a 4:1 dilution but suffice it to say you have w-a-a-y too much.

Why is that? Or is this a chem 201 question? My assumption is that if someone had 200ppm cya and diluted 4:1 the water sample would have 50ppm and be well within range of the test. Is the problem the accuracy of the dilution?

-sent with Tapatalk 2

I'm sure chem geek could answer better than me but since the 1 to 1 ratio of the test is accurate to a +/- 15, I'm sure that a 4 to 1 ratio is significantly less accurate. When you think of it, it's not worth the effort either. Once you're in the 200 range you need to drain 75% of your water to get to 50. Not always doable with an inground pool. Like duraleigh says "you have w-a-a-y too much CYA" and all you can do is start draining as much water as safely possible regardless of an accurate number.

 

[juzzie]

Re: Clarification: CYA dropping due to pool closing/winteriz

The accuracy of the CYA test is worthless in a 4:1 dilution but suffice it to say you have w-a-a-y too much.

Why is that? Or is this a chem 201 question? My assumption is that if someone had 200ppm cya and diluted 4:1 the water sample would have 50ppm and be well within range of the test. Is the problem the accuracy of the dilution?

-sent with Tapatalk 2

I'm sure chem geek could answer better than me but since the 1 to 1 ratio of the test is accurate to a +/- 15, I'm sure that a 4 to 1 ratio is significantly less accurate. When you think of it, it's not worth the effort either. Once you're in the 200 range you need to drain 75% of your water to get to 50. Not always doable with an inground pool. Like duraleigh says "you have w-a-a-y too much CYA" and all you can do is start draining as much water as safely possible regardless of an accurate number.

I am hearing you. Now that I am armed with my TF100 kit I am preparing to go into battle.

My strategy:

1. Empty 75% of water.

2. Refill

3. Get PH level right

4. Shock with chlorine

5. Add borates

Any flaws in my plan?

 

[jblizzle]

Re: Clarification: CYA dropping due to pool closing/winteriz

Draining 75% of the water at once in an in ground pool can be risky ... I am thinking a fiberglass is more risky than gunite as well.

Get your pH right and then follow the shock process.
After passing the 3 tests to stop the shock process, evaluate your TA level and if it is in the correct range, then you can consider adding borates (which are completely optional).

 

[chem geek]

Re: Clarification: CYA dropping due to pool closing/winteriz

If the accuracy of the base test is +/- 15 ppm, then a 4:1 dilution makes the accuracy of your multiplied result +/- 60. So a 50 ppm reading is 200 ppm CYA +/- 60 ppm so anywhere from 140 to 260 ppm. So that's OK for a rough ballpark to know it's pretty high, but not much better than that. If you use a 50 ppm standard to get used to the CYA test, you can probably get closer to a +/- 10 ppm accuracy but with all other possible sources of error I don't think you could get much better than that.

 

[juzzie]

Re: Clarification: CYA dropping due to pool closing/winteriz

As long as you keep putting CYA in the pool, it will continue to accumulate.

The accuracy of the CYA test is worthless in a 4:1 dilution but suffice it to say you have w-a-a-y too much.

Where are you keeping FC?

How does your water look?

I think draining (in steps) that pool is almost mandatory if you want to keep it algae free this coming season.

Oops sorry, didn't answer your question.

Just coming into spring here in Melbourne and the water looks crystal clear.

Been struggling with the pool shop fiasco - throw this in and throw that in, 50 bucks here, 50 bucks there... AAARRRGGGHHH!!!

Short answer free chlorine zero.

I thought my calcium levels were a bit high as well, been using calcium hypo among other things, so I thought just empty and start again?

Or should I do the full suite of tests and post up for more advice? Thought I had no choise but to replace wate when CYA levels too high.

Don't want to treat all my water and then have to get rid of it anyway...

 

[yeggim]

Re: Clarification: CYA dropping due to pool closing/winteriz

Have you ever drained this pool before? jblizzle makes an excellent point in that a fiberglass shell is more prone to float as it has less displacement than a concrete shell.

JamesW expertly explains the mechanics in Floating Concrete or Fiberglass pools

 

[UnderWaterVanya]

Re: Clarification: CYA dropping due to pool closing/winteriz

The accuracy of the CYA test is worthless in a 4:1 dilution but suffice it to say you have w-a-a-y too much.

Why is that? Or is this a chem 201 question? My assumption is that if someone had 200ppm cya and diluted 4:1 the water sample would have 50ppm and be well within range of the test. Is the problem the accuracy of the dilution?

-sent with Tapatalk 2

I'm sure chem geek could answer better than me but since the 1 to 1 ratio of the test is accurate to a +/- 15, I'm sure that a 4 to 1 ratio is significantly less accurate. When you think of it, it's not worth the effort either. Once you're in the 200 range you need to drain 75% of your water to get to 50. Not always doable with an inground pool. Like duraleigh says "you have w-a-a-y too much CYA" and all you can do is start draining as much water as safely possible regardless of an accurate number.

Agreed on drain.
-sent with Tapatalk 2

 

[juzzie]

Re: Clarification: CYA dropping due to pool closing/winteriz

It is my father in laws pool and I spoke to him about draining the pool as I was concerned as well.

He said no worries, it has a hydrostatic valve in the bottom and to go for it.

He also said that the soil is fairly free draining, ie is not likely to hold water.

This all sounds well and good until the fibreglass shell pops out of the ground!

 

[juzzie]

Re: Clarification: CYA dropping due to pool closing/winteriz

Drained 4/5 of the water out. Boorrowed a petrol flexdrive pump from work that drained the 12,680 gallons in an hour. I wanted to drain quick and refill quick.

No problems.

Got three hoses in now filling it up...

Woohoo!