Why Drain Pool with High CYA?

[PoolBryce]

Good morning, everyone.
Six months ago I bought a house with a pool, so I bought a good test kit and got the numbers below:

FC = 24.5ppm
CC = 0
TA = 180 ppm
CYA = 300
CH = 500

It's a 9550 gal plaster pool with cartridge filters and an in-floor cleaning system located in Tucson, AZ.

Based on a lot of reading on this site, I know everyone would tell me to drain the pool (~83% based on PoolMath) and refill to get the CYA down. So my question is why do I need to do this? What's wrong with keeping a really high CYA? The previous owners appear to have just used Trichlor the entire time they owned the pool, and I've been doing the same for the six months I've owned the pool. I add one puck every week or every week and a half, and the pool has been 100% crystal clear the entire time. It appears that the pool chemistry is really stable, and I hardly even have to pay any attention to it at all. So I'm more interested in the philosophy of why keeping a lower CYA is better. I'm not using an exorbitant amount of trichlor with my high CYA, so I guess I don't see a problem with these numbers. I really appreciate your thoughts on this.

A related question is whether it's safe to swim in a pool with these numbers. I swam in it for a few months before winter with no ill effects.

Thanks in advance everyone!!
Bryce

 

[YippeeSkippy]

Hey there Bryce

One element you didn't mention is your pH. Continued use of pucks will drop your pH pretty low as they're acidic. If the pH is too low it wreaks havoc on a lot of equipment and the pool surface itself.

If you ever have an algae problem you'll be hard pressed to fix it because the amount of chlorine it will take to overcome that high CYA is really ridiculous.

Yup, I'd say drain and refill.

Maddie

 

[mknauss]

And with FC above 10 you cannot test your pH accurately.

Very curious on what test kit. To get a CYA of 300 you would have had to do a 1:4 dilution. So your results are, at best, +/- 50ppm

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Take care.

 

[Jimrahbe]

Bryce,

The key to operating with a high CYA is to have really high FC...

The main problem is when your CYA is 300 and you try to maintain an FC of 2 or 3 ppm... That is when you can hang the "Algae Party this weekend" sign in your front yard.

Thanks,

Jim R.

 

[JoyfulNoise]

When water has high CYA levels in it, the concentration of active chlorine (hypochlorous acid) is extremely low, less than 50ppb (0.05ppm). Hypochlorous acid is your primary water sanitizer that stops person-to-person disease transmission. So, even if your water stayed algae free, the active chlorine levels are so low that there’s nothing protecting you from the diseases carried by other bathers in your pool. Should another bather enter the water with an active infection, everyone in the pool can be exposed. Not necessarily bad within a single family but pretty bad if you plan to have a party.

 

[mdogan]

Just wondering which test kit you used and get CYA 300? most of reliable CYA tests are up to 100.
Without knowing PH in your pool rest are numbers useless, but if FC is over 10 that is also not possible.

If your TA is 180, that mean your PH able to go up or down like rollercoaster.

most of document write like this,
Suggest FC amount in the pool; 2-4ppm...all this documents consider that CYA 30.

Your pool is crystal clear since you are using weekly shock and good luck.
if everyone start using Liq Chlorine Pool companies will be bankrupt

 

[needsajet]

While technically possible, it's certainly not TFPC to run a pool at 300 ppm CYA. So TFP guides and experts are not in a useful position to provide advice.

You can drain with little to no risk, and the cost isn't very much. If you decide to drain/refill, here's what I would think about.

Some utilities use your winter water consumption to set sewer rates. If they do, wait until after the months used for that estimate, or call and ask them to waive it by the amount of volume for your pool. If not, you'll pay excessive sewer rates for the upcoming 12 months until a new winter consumption number. By calling, some people have even achieved waiving of the top tier water rate, so the call is worthwhile. Cost to fill a pool varies widely, but typically, residential pools fill for $100 or less, but it's a good idea to know ahead of time what your cost will be.

This time of year the pool water is probably colder than what comes out of your tap. It's certainly saltier than tap water, so the pool water is heavier (more dense) than your tap water. You can close off your skimmer(s) and pump water to waste from the bottom (main drain or separate submersible pump). Simultaneously, put a garden hose in the skimmer, wedge the weir flap down, and fill from there, so the fresh water floats gently out onto the surface. Minimize disturbance of the water, e.g. don't brush, or have any water coming from return jets, cleaning systems, shut off spillways/features, remove any pool cleaner, etc. Match the flow so you can let it run overnight. If you can't match it enough, let it fill nearly to the coping, then drain down to an inch or so up from bottom of skimmer throat, fill it up again, drain, repeat, etc., but pick days so you can keep it all going through to the end. Keep doing it until you see lower CH, CYA, or Salt (depending on what tests you have) in the drain water. Then return to normal, mix it all up, and see where it's at.

At the very least, you'll save money on test reagents. I suspect you'll eventually save on chemicals as well, because of the high chemical cost if the pool gets cloudy or green, or by avoiding regular shocking which usually is just a waste of chlorine. How you manage without knowing pH, I don't know, but chances are it's lower than what you're seeing in a phenol red test, because of the high FC confounding the pH test.

 

[kimkats]

While you have a plaster pool and I have a vinyl one the unbalanced water can still cause problems. I ruined my first vinyl liner due to HIGH cya and low pH. The water was clear but NOT fun to swim in. Our eyes hurt and were red after swimming. Our skin did not like it either once we got out. It felt "tight" and dried out. My liner "dry rotted" for lack of a better term.......I found a small crack on the bottom with my toe. I messed with it to see what was going on. That caused the WHOLE bottom of my pool liner to crack. This allowed ALL of the water to rush out of the pool, almost taking me with it!

You can do with your pool what you wish. It has worked this long so.......We will be here when something happens (my guess an algae outbreak or plaster doing weird stuff) to help you fix it back up.

Kim

 

[duraleigh]

What's wrong with keeping a really high CYA?

1. You lose a certain percentage of FC regardless....say 25% daily roughly at normal CYA levels

So 25% of 24.5 is about a 6 ppm loss

25% of a normal level of FC say about 4-6% is a 1.5 ppm loss

You are wasting FC

2. Your continued use of pucks adds CYA continuously so you will soon be unmeasurable and unmanageable.......guaranteed.


Stop your puck usage and drain your pool to reduce CYA to around 60 ppm. It's only a matter of time before your pool becomes quite troublesome.

 

[Rollercoastr]

Is anyone else surprised by a pool in AZ with sky-high CYA, but only "high-ish" CH?

 

[JoyfulNoise]

Is anyone else surprised by a pool in AZ with sky-high CYA, but only "high-ish" CH?

No. Depends on what your input water is and if one is chlorinating with pucks. Trichlor use in this area is huge - all the service companies use it and people walk out of Costco’s here with palette carts loaded up with 35lbs buckets of Clorox Ultra-Blue X-in-1 tablets whenever they go on sale. Input water can be hard (municipal) but a lot of folks are on wells or softeners and their fill water can be very low in CH.

 

[Rollercoastr]

Interesting. I figured that high CH was just a fact of life down there.

 

[richierich]

It's interesting, my neighbor has an inground pool. She rarely tests and just throws some pucks in the floater. She's been doing this for 10 years. She says a couple times a year she shocks the pool. Her water is kind of clear. I mean I can see the bottom but it always looks a little cloudy with almost like a blue-green tinge, not crystal clear though. I don't know how she doesn't have a massive algae outbreak but she doesn't. My kids went swimming in her pool last year and were like amazed how much clearer my pool was. Mine is almost like water from a bottle. My neighbor probably doesn't even know how clear the water truly can be. She's been pool stored. So what I'm saying is yeah it can be done, but its definitely not the right way.

 

[Swampwoman]

Hi Bryce, and welcome to tfp I just wanted to emphasize this aspect of your question

So I'm more interested in the philosophy of why keeping a lower CYA is better.

A: To kill water-borne pathogens.

Matt alluded to this but I think it bears emphasis. The founding science behind the TFP philosophy is that your FC (free chlorine) should be kept at 7.5% of your CYA for optimal sanitization. The industry is slowly adopting to the standard, and finally recognizing the research that shows that very high cya levels reduce the efficacy of FC.

Please see the [fc/cya][/FC/cya] for reference. If you elect to follow the chart, you will soon see why cya of 300 is considered unmanageable.

 

[JoyfulNoise]

It's interesting, my neighbor has an inground pool. She rarely tests and just throws some pucks in the floater. She's been doing this for 10 years. She says a couple times a year she shocks the pool. Her water is kind of clear. I mean I can see the bottom but it always looks a little cloudy with almost like a blue-green tinge, not crystal clear though. I don't know how she doesn't have a massive algae outbreak but she doesn't. My kids went swimming in her pool last year and were like amazed how much clearer my pool was. Mine is almost like water from a bottle. My neighbor probably doesn't even know how clear the water truly can be. She's been pool stored. So what I'm saying is yeah it can be done, but its definitely not the right way.

Next time you happen to be near their pool, grab a water sample and see what it looks like....you might never let your kids swim there again

Her approach to pool care is pretty standard - throw in whatever the pool store tells you too and hope for the best. Given that you're on LI (from where my peoples come...), you get enough annual rain dilution and snow melt to make most CYA problems manageable. As long as the pool is getting enough fresh water exchange each year, I bet her CYA levels are fairly low to start with and then climb throughout the summer only to have them go back down when the pool is drained for winterization and then refilled over the winter. Pucks can work in a climate like that as long as one is careful to consistently push up their FC as the CYA increases. The occasional shock is probably just enough to keep anything really bad from happening especially if cal-hypo is used instead of dichlor.

 

[richierich]

Next time you happen to be near their pool, grab a water sample and see what it looks like....you might never let your kids swim there again

Her approach to pool care is pretty standard - throw in whatever the pool store tells you too and hope for the best. Given that you're on LI (from where my peoples come...), you get enough annual rain dilution and snow melt to make most CYA problems manageable. As long as the pool is getting enough fresh water exchange each year, I bet her CYA levels are fairly low to start with and then climb throughout the summer only to have them go back down when the pool is drained for winterization and then refilled over the winter. Pucks can work in a climate like that as long as one is careful to consistently push up their FC as the CYA increases. The occasional shock is probably just enough to keep anything really bad from happening especially if cal-hypo is used instead of dichlor.

haha I don't want to know what's in that pool. But yeah I'm figuring that's what keeps the CYA manageable. Mine is 10x clearer than hers

 

[PoolBryce]

Hi everyone,
Thank you for all the responses so far, and sorry for the delay in replying; my work schedule was crazy this week. I guess I forgot to post my pH originally, but it was 7.8 when I took all those other measurements.

So I'm basically convinced I should drain and refill per the PoolMath calculator (drain ~83%). Can you point me to any great threads for what to do immediately after re-filling (such as what chemicals to add immediately)? I want to have a plan before I do this. I'd also like to have an idea what chemicals to have on hand.

One other question I have related to this is: if after I refill I stop using pucks and start using liquid bleach (which seems to be the preferred approach here), it seems to me like this method requires daily water tests and daily inputs of liquid bleach. What do you do when you go on vacation for a week? And what happens if life gets in the way, and you don't test or put bleach in for a few days? If I can't commit to daily testing, and I better off sticking with pucks? At least the pucks seem to be set-and-forget for a week or so at a time.

Thanks again! This has been super helpful for me!
Bryce

 

[mknauss]

You will need muriatic acid, liquid chlorine, and potentially CYA powder. The latter only if you over drain.

You are correct if you plan to add liquid chlorine daily, it needs to be done EVERY day during the April to November time period. If you are gone for just a few days, you can probably use pucks to cover those days just being sure to account for the CYA rise from them in your ongoing FC maintenance.

You can continue to use pucks. You would most likely need to drain 1/3 of your water each month during the spring/summer/fall months. Your CYA and thus your FC requirements will yo-yo. Not very efficient.

You can install a tank and Stenner pump for the chlorine. You can then get away with only adding liquid chlorine to the tank every few days. You will still need to test to be sure your additions by the Stenner are adequate.

Or, you can install a SWCG. It will create your chlorine on a daily basis. After fine tuning, you can get away with only testing every few days to eventually once a week. You need to monitor your pH and CSI often. You will be adding acid weekly or so.

We leave for extended periods. We have a pool service that comes by once a week and cleans the pool, adds acid, and adjusts the SWCG schedule if necessary. I have a camera on the pool and can tell if the FC or pH is not being maintained by the look of the water. But that takes time to get to that point.

Hope that helps.

Take care.

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[cfherrman]

Vacation is easy, have slightly lower cya and toss a puck in. A puck or two won't build the cya too much.

Tfpc is all about knowing exactly what you are doing to your pool. Use pucks all the time is a setup for failure.

Using bleach takes maybe a week of getting used to then you can start testing every other day, but yes you must test often but then it's a 100% that your pool is safe and won't green up. With pucks your pool is never 100% safe.

 

[Demegrad9]

To the vacation question: CYA naturally decreases slowly over time because of water replacement (splash out, backwashing, vacuuming to waste,...) and you refill with zero CYA water. People usually just deal with the reducing CYA until vacation, load up a floater with Trichlor pucks and toss it in which both slowly releases chlorine and helps get CYA back up.

On the time issue, that's why most of use get a SWCG or a stenner liquid chlorine injector. In summer I usually check FC and pH every two days, but I only make adjustments every two to three weeks.