Killer CYA - Stuck - HELP!

texas_scot

Member
Sep 2, 2019
8
Austin, TX
Unfortunately I only stumbled across these forums a few weeks back. We inherited our pool when we purchased our house in July 2015. It was originally built with a SWG, but the previous owners had converted to chlorine tabs due to the limestone surround being eaten by the salt. We had a few ups and downs with algae and pollen over the last 3 summers, but generally the advice from the Leslie's guy was effective. One other point of note, I added a UV unit so that I could run with FAC around 2%.

This summer we had the misfortune of our erosion chlorine feeder stopping working maybe 1 or 2 days into a 14 day vacation. We came back home to a very green pool. We shocked, algae killed and cleared the water using the requisite Leslie's recommended chemicals, and I managed to get the pool back to crystal clear in time for a swim party a few days later.

The problem is that since then we've not been able to keep the FAC level much above zero and had at least three more recurrences of algae growth. No doubt the 100 degree heat and zero rain for the last month has been a contributing factor. At least 5 shock treatments later, with the Chlorine feeder set on max (6 3" tabs every 3 days), and still no FAC, I started googling for a solution and came across TFP. I performed an overnight chlorine test - raised the FAC to 2% using liquid chlorine at 9pm and measured it below 0.5% at 7:30am the next morning...

Based on that data, it appears that I have a problem that needs to be SLAMed. I began to plan my strategy. I ordered a Taylor K-2006 test kit, and picked up 15 gallons of 10% chlorine from Home Depot. That quantity was based on the CYA level reported by Leslie's (80ppm), and my 33,000 gallon pool. Unfortunately once the Taylor kit arrived, my first CYA test reported a level that is way north of 100. It now looks like I need to spend around $400 on a partial drain and refill ($140 for a pump and hose, $250 for water).

Before I go down that path, are there any other ideas out there? If not, does anyone have an opinion on this pump: XtremepowerUS 1/2 HP Dirty and Clean Water Submersible Thermoplastic Utility Sump Pump 25 ft. Cord-71048-XP - The Home Depot.

It looks pretty basic, but it only has to run for 10 hours, after which I hope to never use it again :)

Also, if I don't want to reinstate the SWG, what are your recommendations on how to maintain the chlorine level after the SLAM is over? I am fine to add liquid chlorine 3 or 4 times per week based on test results, but if I am gone on a business trip, it is probably more than my wife would sign up to. She is a trooper and looks after the skimmers and brushes etc. She even helps clean the filters. But she may baulk at handling liquid chlorine.

One final point - I guess I could wait until it gets cooler / more rainy, and allow nature to dilute the CYA some. And do the partial drain / re-fill in the spring when I am not running sprinklers and water is cheaper. But I don't know what I would do in the meantime - could I use Potassium Monopersulfate shock + the UV to keep the pool sanitary until the temperature cools down? I could add liquid chlorine before any swimming / hot tub usage to make sure things are safe.

Thoughts / comments?

Thanks
 

Flying Tivo

Well-known member
Jan 24, 2017
1,152
Monterrey, NL, Mexico
You need to do the diluted CYA test. 50% pool water/50% tap water. Then multiply your results by 2. I also think you need to drain water but wait until you do the diluted test so you know how much to drain. You dont need to buy a sump pump, you can rent it at HD or Lowes just for the time needed. Th UV thing is worthless, you do not want to use MPS shock it will interfere with CC testing. SWG do not eat limestone.
 

frogabog

Gold Supporter
LifeTime Supporter
Jul 16, 2010
2,833
Portland, Oregon
Might want to tell your wife that liquid chlorine is bleach. 10% for LC, 6% for bleach that you buy in the grocery store. It's really only dangerous to her clothes and if you pour it in close to the water it won't splash. I'm going to assume she's used bleach before, maybe for household cleaning?

You also may want to check your pool's salt content. If you've been using chlorine after the previous owners used chlorine for years, you probably have close to what you need in your pool (salt wise) to just turn on the SWCG and let it do the job of making chlorine for you. When chlorine is used up, what's left is salt. I think you'll be surprised at how much salt you already have in the water.

It wasn't the salt that ate the limestone... it was improper water chemistry.
 

texas_scot

Member
Sep 2, 2019
8
Austin, TX
So I did the 50% CYA test and it showed somewhere between 85 and 90 implying 170 to 180 ppm. Does that mean I need to pump out 75% of my pool? Are there any other chemical imbalances that could pull the CYA number off?
 
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frogabog

Gold Supporter
LifeTime Supporter
Jul 16, 2010
2,833
Portland, Oregon
So I did the 50% CYA test and it showed somewhere between 85 and 90 implying 170 to 180 ppm. Does that mean I need to pump out 75% of my pool? Are there any other chemical imbalances that could pull the CYA number off?
Nope. Other than the subjectiveness of the test (your eyes), cuz CYA is CYA.
 

jlt19

Well-known member
Aug 20, 2019
47
St. Louis, Missouri
I was in a similar position with a high cya (160) and algae bloom. However, we'll be closing within the next month so I didn't want to rent a pump to drain now, only to have to do it again at closing. Also, we only get a few hours of direct, no longer hot sun so I'm hoping cya will lessen over the winter.

All that said, I did a deep clean, while vacuuming to waste and lost quite a few inches. This dropped cya to 140. I was easily able to bring FC up to 55 (SLAM level) and am almost done. I'm ok maintaining it at 17 until I close.

So, it's doable at such a high cya, but may not be such a good idea in your situation.

As far as your wife and the chlorine. That's the easiest part of maintaining the pool, imo. We were out of town over Labor Day and I just asked my dad to pour a gallon in each day. Even if it was more than needed, it was better than nothing and I didn't want to make him measure.
 

BowserB

Silver Supporter
Jul 29, 2018
184
Katy, Texas
Scot, I didn't pick it up from your posts (could have missed it, though), but you do know that the regular chlorine tabs add CYA to the water, and you've stopped using them...right? You can buy calcium hypochlorite tabs which don't have cya, but they do add a bit of calcium to the water and are very expensive ($130 for 50 lbs of 70% chlorine tabs at Amazon.) I use liquid chlorine but considered those for when I'm away. Also, I have both ozone and UV-C, but I maintain chlorine levels as though I did not have them. Consider them as extra protection, like having Norton antivirus plus Malwarebytes. I know there is valid science behind the UV-C (which btw you cannot get from the sun, as UV-C is absorbed in the atmosphere), and UV-C kills cryptosporidium, which is not affected by chlorine.) If you have pool parties, especially with kids, crypto is a valid and growing concern. Ozone can be beneficial too, but it depends on where it enters the water flow.

Back to the CYA. I had it drop over the winter, and I've heard the same from others, but no one so far has explained what happens to make it drop without exchanging water. If the mystery of the winter CYA drop could be explained, we might learn another way to reduce it. A neighbor down the street has a chiller for his pool water (what do you think of that, New Jersey or Winnipeg? My pool water has been 92-93 degrees most days for the last month and a half; finally dropped to 91 today), so if cold is the answer, maybe some kind of rented refrigeration unit or a truckload of crushed ice would work for a one time CYA reduction?
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
11,838
Northern NJ
You can buy calcium hypochlorite tabs which don't have cya, but they do add a bit of calcium to the water and are very expensive
Calcium hypochlorite, in the solid form, shall not be mixed with other pool chemicals including other chlorinating agents.

Do not put cal hypo tablets in any floater or feeder used for trichlor or dichlor.

Back to the CYA. I had it drop over the winter, and I've heard the same from others, but no one so far has explained what happens to make it drop without exchanging water. If the mystery of the winter CYA drop could be explained, we might learn another way to reduce it. A neighbor down the street has a chiller for his pool water (what do you think of that, New Jersey or Winnipeg? My pool water has been 92-93 degrees most days for the last month and a half; finally dropped to 91 today), so if cold is the answer, maybe some kind of rented refrigeration unit or a truckload of crushed ice would work for a one time CYA reduction?
It is not cold temperature that degrades CYA in the winter. It is dilution and/or bacteria.

 

texas_scot

Member
Sep 2, 2019
8
Austin, TX
Thanks for the great suggestions everyone. Yes I do know that the regular tabs add CYA and I have gone cold turkey since mid last week. Right now I am treating the pool as being ‘closed’ until I figure out my strategy. I plan to do a 4:1 dilution CYA test later today to try and get a more accurate take on the level. I am also considering to do a 1gal test to see how much Cl I need to add to get to the mid 30s and stay there. I will update the thread later.
 

texas_scot

Member
Sep 2, 2019
8
Austin, TX
4:1 dilution test came out between 40 and 45... So 160 to 180ppm CYA.

Gallon test at 71ppm FAC underway overnight.

I have a question about SLAP - if I had SWG, recommended CYA level is ~80ppm, but SLAP isn’t recommended at that CYA level. Am I misreading something. It makes a big difference in how much pool I need to pump out.

Also, per the prior post about doing a water exchange - is there any concern with pumping out a pebbletek pool and not refilling it simultaneously?
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
11,838
Northern NJ
4:1 dilution test came out between 40 and 45... So 160 to 180ppm CYA.
I think your CYA is 320+. 40 - 80 - 160 - 320 is 4X dilution.

I have a question about SLAP - if I had SWG, recommended CYA level is ~80ppm, but SLAP isn’t recommended at that CYA level. Am I misreading something. It makes a big difference in how much pool I need to pump out.
You need to pump out 80% to get around CYA 70 or 90%+ for CYA 30. You are not going to be that precise anyway. Go for 90% and see where you end up. Easier adding some CYA then needing to drain again.

Also, per the prior post about doing a water exchange - is there any concern with pumping out a pebbletek pool and not refilling it simultaneously?
Water exchange is based on pumping out and filling simultaneously with a balanced flow out and in.
 

frogabog

Gold Supporter
LifeTime Supporter
Jul 16, 2010
2,833
Portland, Oregon
You don't have a SWG, therefore your chart is the non SWG CYA chart.

SLAM is cheaper and uses less chlorine at lower CYA levels. 30ppm is ideal. If you have to SLAM, you can do it at higher CYA but it just takes that much more chlorine to do the same job. You can always add more CYA if you decide to drain it enough to get to 30ppm. In your area, 50-60ppm CYA is generally needed for regular maintenance.

Yes, there is a concern about draining any inground pool if your area has a high water table.
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
11,838
Northern NJ

texas_scot

Member
Sep 2, 2019
8
Austin, TX
Our house is on top of a hill, built on rock. Is there really any danger of the pool ‘floating ‘?

Also I did a 1 part pool water, 3 parts tap water dilution for the CYA test. So I think that 4x40=160 or 4x45=180 is the correct level.

In any case, 75% pump-out = 25K gal at ~14.50 per K gal = $362.60 + pump rental or 23 gal of Cl from Home Depot at ~$3 /gal = $69. Am I missing something?