CYA, please:) (I'm sure you've been asked this before!)

MaryJo

New member
May 7, 2021
3
Pottsboro, Texas
I'm new and should've paid more attention in chemistry class!! We live in North Texas. (close to Okla) and have a 13,000 gal fiberglass pool with sand filter that came with the house. House was built in 1998 and we've been the owners since 2013. We had a high cya number last summer, but were told that it was OK.....The number didn't decrease over the winter (even with our severe cold snap and 4" of ice on top!) Currently have 110 as cya and no chlorine! We've done some amounts of draining to 'waste' a few times and managed to lower cya from130 down to the present 110. We've had about 4-5" of rain recently and were hoping that would help. With warmer weather coming I'm seeing a little green developing! Hubby will get a pump tomorrow and we will drain more of the pool but will have to drain to street as we are on the low side of our neighborhood and have saturated ground already. Sooooo...hopefully, we can lower the cya over the next couple of weeks? My question to you all......What should I be adding to keep some sanitizer or algaecide in the pool until we can do a significant enough drain to lower the cya? Is diclor the only culprit to cya??
 

zea3

Mod Squad
TFP Expert
LifeTime Supporter
Jul 10, 2009
13,794
Houston, Texas
Hi, welcome to TFP! Dichlor powdered shock and trichlor tablets both add CYA to the pool. Stick with liquid chlorine for now. It wont add anything you don't need to the pool.
 
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needsajet

TFP Expert
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Jan 4, 2016
4,930
Sydney, NSW, Australia
Pool Size
44000
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Plaster
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Salt Water Generator
Welcome to TFP! Good to have you here :)

Dichlor will add too much CYA, yes, and also trichlor (the hard form like pucks or tablets).

Only use liquid chlorine as you hold the algae at bay, either swimming pool chlorinating liquid or plain bleach with the % listed on the label, and 10% sodium hypochlorite or greater. Bleach and pool chlorinating liquid are the same thing, so it's just a matter of price. Any bleach that you buy should have no additives such as anti-splash or scents.

The only way to properly clean up algae is by this method: SLAM Process and you're going to need to get down to around 70 PPM or less CYA. Otherwise you'll be freaked by the enormous amount of chlorine needed.

To do that method, you need to learn some pool chemistry ABCs of Pool Water Chemistry

And have a proper test kit: Test Kits Compared

When pumping the pool out during or after a rainstorm, try to take water from the bottom without or before the pool pump is able to mix the water up.

It's really great that you're getting started on this early in the season. Every chance you'll have a trouble free pool for the summer. :)
 
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TexEdmond

Gold Supporter
Jun 16, 2021
67
Edmond, OK
Pool Size
26000
Surface
Plaster
Chlorine
Liquid Chlorine
Hi, MaryJo!

We were in a very similar situation, but our CYA was 153. You're correct that draining and refilling is the only option. I drained what we thought was about half of the pool and refilled (it was more like 25%) , only to see a 32ppm reduction in CYA. I drained it again this week down to past 50%, and our current CYA is around 59ppm.

My wife was quick to point out, draining more out of the pool the first time is clearly the more effective method rather than multiple smaller drains. At first I didn't understand her point, but it totally clicked when I thought through it. When I drain 10% of the pool and refill it, that'll give me one number for CYA reduction. If I drained and refilled again with the same percentage of water, I'm not draining the same amount of CYA, because the overall concentration is lower. Thinking about it the other way around, what I'm doing is actually draining some of the fresh water I refilled with last time. It's not a huge factor for our house because we don't have as bad an issue with getting rid of excess water, and we're on a well, so it's not costing us a fortune to run water thru a meter into our pool. The biggest hassle for me is the time commitment to the thing, because the amount of water I drained and refilled the second time (approx 13k gallons) was almost the total capacity of your pool. That second dump got us from 121ppm to 59ppm CYA.

I'd recommend ripping off the band-aid, and going for a bigger dump. It'll be cheaper and faster in the long run to get you to the levels you want.

Good luck!
 
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mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
41,454
Laughlin, NV
Pool Size
6000
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Chlorine
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Pentair Intellichlor IC-40
I'd recommend ripping off the band-aid, and going for a bigger dump. It'll be cheaper and faster in the long run to get you to the levels you want.
Do be ware the OP has a fiberglass pool. They can pop out of the ground very easily if drained too far.
An Exchange is safer with most pools, but especially fiberglass or liner pools.
 

TexEdmond

Gold Supporter
Jun 16, 2021
67
Edmond, OK
Pool Size
26000
Surface
Plaster
Chlorine
Liquid Chlorine
Do be ware the OP has a fiberglass pool. They can pop out of the ground very easily if drained too far.
An Exchange is safer with most pools, but especially fiberglass or liner pools.

I see. Too big for my britches, I hadn't considered their whole situation. Thanks for correcting me.
 
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TexEdmond

Gold Supporter
Jun 16, 2021
67
Edmond, OK
Pool Size
26000
Surface
Plaster
Chlorine
Liquid Chlorine
They can pop out of the ground very easily if drained too far.
There's a similar phenomenon up here in Oklahoma with incorrectly installed tornado shelters popping up and having to be reburied after heavy rains. Years ago the soil around my aunt and uncle's house in Georgia was so saturated by a hurricane that the liner of their in-ground pool was bubbling up from the inside and never laid back down flat again because it had stretched. Buoyancy and hydrostatic pressure are so bizarre.
 
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MaryJo

New member
May 7, 2021
3
Pottsboro, Texas
Thank you all! Sorry for my delay in responding:) Earlier in the spring we were hoping that the people who recoated our pool a few years ago would be able to come back to fix some 'chips' on the bottom. That way we would be able to drain, paint and fill...and start over! However, our spring became a flood season and we were definitely afraid of having the pool pop out! The fortunate thing about the rain was that we were having to drain every few days anyway....So we took advantage of the weather! I used the pool calculator (love it!) and kept the pool adjusted. When it overflowed, we drained it down. All that water collected at the lower end of the yard away from the pool! Yes, it's been a slow-go, but we are almost there! CYA is presently 73...still a little high. We are presently having to add water due to increased swimming splashes and evaporation, so when the weather is drier, I'll do some more draining:)
 
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