New Pool Owner - CYA w/ new SWG

Andrewdgwood

Member
Jun 16, 2019
5
New Jersey
Hi all,

Bought a house with a pool last year and this forum has been very helpful. This year decided I would invest in a SWG and attempt to drop the CYA to get things in line with the recommendations on this forum. Thank you in advance for your help.

1. We have a plaster pool that apparently lifted 1-2 times with the prior owners during a drain. To mitigate some risk I had a professional lower the pool ~2 feet 2x last week to lower the CYA. Pool is fine but it looks like CYA is still high. I did the CYA test multiple times at 50% / 50% dilution (fresh / pool) and 100% (pool). I'm struggling a bit to determine exactly just when the dot "just" disappears but I believe it's around 120 (definitely over 100). To avoid another partial drain and refill, could I work with this CYA and hope it slowly lowers over the season with backwashes / rain? If I need to maintain a FC of 4.5% of the CYA (SW pool), I'm hoping the SWG should be able to produce a FC of 5-7, which should be sufficient. We have a 40k Hayward cell for a 25k pool. I can occasionally add chlorine as needed as to not set my SWG % too high but I do not know if this is unreasonable since it's new.

2. What are the risks of using dry acid? I have chemical sensitivities and was really hoping to use dry acid. What is the best way to add this to a plaster pool (dilute first, direct into deep end, etc.)?

3. What is the correct order to address my low TA / high PH? Do I address the TA first and then wait a few hours before lowering the PH?

4. Given my CH is low, could I continue to use calcium hypochlorite on occasion if needed if the FC drops too low?
  • The size of your pool in gallons ~25k
  • If your pool is an AG (above ground) or IG (in ground) - IG
  • If it's IG, tell us if it's vinyl, plaster/pebble, or fiberglass - Gunite (plaster)
  • The type filter you have (sand, DE, cartridge) -Sand
  • List any other equipment you have: SWG, second pump, etc. - Recently installed SWG
  • List what test kit you use to test your water - K2006
  • Location - NJ
FC - 9.5 (added 4 pounds of 73% Calcium Hypochlorite 48 hours ago, shorty after opening pool, SWG set at 47%)
CC or TC - 0
pH - 8
TA - 70
CH - 170
CYA - 120
 

kellyfair

Gold Supporter
Bronze Supporter
Jun 29, 2016
2,925
Tampa, FL
If it were me, I would much rather lower my CYA within recommended range, than put the wear and tear on my salt cell. Make sure you are only glancing in the tube, not staring into it. If you do decide to live with the high CYA, you might consider supplementing with chlorine rather than let your salt cell carry the load.

I would do as you suggest - raise TA, then lower PH. May have to do a couple of times until both are where you want them. I don’t use dry acid, so will let someone else answer that.

Also, you need to watch your CH since you have a plaster pool. I’ll let someone else speak to that.
 

mguzzy

Gold Supporter
Jul 8, 2015
2,393
OV, CA
1. Sorry I think another Drain refill is in your future. at 120 you will have a lot of Cl locked up in the CYA. You don't need a pro to do it, its quite simple. If your pool is prone to floating do the no drain water exchange: Draining - Further Reading

2. Dry acid adds sulfates which accumulate in the water.. it's better to use Muriatic Acid. But if you use dry acid, yes you predissolve it in a bucket. Acid - Further Reading

3) I think your TA looks fine for a SWG pool. ,What Are My Ideal Pool Levels? - Trouble Free Pool

4) Yeah if you already have some laying around. If you have to buy some just get the Calcium Chloride.. it will be faster.

Obviously all the fine work you did getting your levels adjusted will have to be done again after you exchange water.
 
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Andrewdgwood

Member
Jun 16, 2019
5
New Jersey
Thank you both!

The prior owners left a submersible pump. I would just need to get a hose long enough to drain to the street. Presume I just turn the filter off, put the pump in the shallow end and let it run? Do I need to make sure the chlorine has dropped first before I pump the water out to the street?

My preference would be to give it a shot with the 120 CYA by running the SWG on a reasonable percentage and adding chlorine manually as needed to maintain a FC of 6 and see where the CYA is at the end of the season. At what % am I putting wear and tear on the SWG? Is this a horrible approach?

Regarding the CYA test, has anyone had an easier time using the pentair test with the moving stick?

Many thanks again for your help.
 

mguzzy

Gold Supporter
Jul 8, 2015
2,393
OV, CA
Thank you both!

The prior owners left a submersible pump. I would just need to get a hose long enough to drain to the street. Presume I just turn the filter off, put the pump in the shallow end and let it run? Do I need to make sure the chlorine has dropped first before I pump the water out to the street?

My preference would be to give it a shot with the 120 CYA by running the SWG on a reasonable percentage and adding chlorine manually as needed to maintain a FC of 6 and see where the CYA is at the end of the season. At what % am I putting wear and tear on the SWG? Is this a horrible approach?

Regarding the CYA test, has anyone had an easier time using the pentair test with the moving stick?

Many thanks again for your help.
-Yep that's what you do on the drain. check the codes for you area. some will specify drain to the street some want you to drain to your sewer clean out. You want to get it down to below 80 with a SWG

-Trying to run with a CYA of 120 will be a losing proposition. With a CYA of 120 you will have maintain a very high CL and you will have a hard time keeping the pool sanitized since so much Cl will be locked up in the CYA. see this chart: FC/CYA Chart.
 

Andrewdgwood

Member
Jun 16, 2019
5
New Jersey
All makes sense. Where I'm hesitating a bit is that I've seen TFP recommends that FC be 4.5% of the CYA level for a salt water pool. If my CYA is 120, I would need to maintain a FC of 5.5, which doesn't seem that high. Totally understand that the CYA should be lower, just wondering if it would be possible to save myself the hassle and a ton of water and let the CYA drop slowly over time via backwash and rain. Perhaps a FC of 5 will be difficult to maintain - just trying to run through my options before we drain for a third time and rebalance again. Thanks again
 

mguzzy

Gold Supporter
Jul 8, 2015
2,393
OV, CA
Yeah you could do that, but you really have to stay on top of things. Do you get a lot of summer rain in your part of Jersey.. the parts I've been to always seemed to have drizzly summers. If you know a good storm is coming drain some off water and let it refill. That will bring it down faster than just letting it overflow. CYA will degrade slowly in the heat, that seems more an issue in the southwest with the blazing hot they have in the desert. Just be aware that the higher the CYA is, the less effective the chlorine is. And at some level you reach a point of diminishing returns. That's when once algae gets a foot hold you can't keep enough FC in the water to kill it.

So yeah, you could limp along with that and keep and eye on things Or if you want to be done with it do a water exchange. either way will work, just whatever you are comfortable with.
 
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kellyfair

Gold Supporter
Bronze Supporter
Jun 29, 2016
2,925
Tampa, FL
Wait a second... the target for CYA of 120 isn’t 5.5... that isn’t even the minimum recommended FC. You would shoot for FC of 9, with CYA at 120.
 

Andrewdgwood

Member
Jun 16, 2019
5
New Jersey
Thanks both. It seems like recently we've been getting heavy rains here in NJ. FC was 7.5 today with the SWG running at ~50% although it has not been very hot.

Regarding the min FC of 5.5...I was going off this chart and the foot note:


"Most saltwater chlorine generator (SWG) pools appear to prevent algae at a minimum FC level of 4.5% of the CYA level as compared with the roughly 7.5% of the CYA level shown in the "Min FC" column for manually dosed pools."
 

kellyfair

Gold Supporter
Bronze Supporter
Jun 29, 2016
2,925
Tampa, FL
I think you must be looking at an older page... click on the link in my signature for the chart and you’ll see it doesn’t have that specific reference. Also, I believe the percentage you refer to is for minimum... target should be a tad higher than that.

Best way to determine is to use Pool Math app on your phone. It will tell you what to shoot for AND what to add to get there (or what setting you will need for your SWG).
 

Andrewdgwood

Member
Jun 16, 2019
5
New Jersey
Thanks Kelly. I plugged the the 120 CYA into Poolmath and the FC range is between 6 - 15. I redid the tests after the pool was running for a few days (also had some rain) and I think the CYA is actually closer to 100. I'm running the pump 12 hours a day w/ the SWG at 45% and my FC is 7.5. I'm prepared to manually dose chlorine should that be needed. I'm going to try and let the CYA diminish on its own this summer and hopefully when we open the pool next year we are closer to 80. Many thanks for your help.