Covered indoor pool Combined Chlorine dissipation/distruction

dstutto

Member
Feb 25, 2021
19
NY
Pool Size
3000
Surface
Vinyl
Chlorine
Liquid Chlorine
I have recently started a 3k gal endless pool in my basement. Water was added over 5 days from the municipal water supply. I finished filling it about 5 days ago. I also added about 13 cups of chlorine over the 5 days. My Taylor k-2005 kit was about 15 years old (it's a 2nd hand pool) and most of the test were ineffective. However, the TA seemed to be very low (about 20ppm) and I added 4lbs of Baking Soda, which boosted it to about 140. Whoops. The chlorine was off the scale of my 2nd cheapo test kit (that test kit was also about 15 y.o.).

The next day (3 days ago) I took a water sample to Leslie's and received the following analysis:
PH:8.1
TC: 7.91 FC: 6.04
TA: 138
CH: 16
CYA: 5
TDS: 500
Iron: .1
Phosphates: 284

I left with some PH down, Calcium hardener, MPS, "Culator" (mineral remover for the iron). I added 19.5oz of pH down, which dropped my pH to 7.0 and my TA to about 110 (with the old test kit). I ran my hydro-therapy jets for about 30 min to aerate the water and bring up the pH. It came up to about 7.5 yesterday and has dropped a little today (7.2 or so). I ordered a new k-2005 test kit from Amazon and also the TF-100. Both kits arrived in the last day, and I took a new water sample back to Leslie's.
The home test kits indicate my water as follows:
PH: 7.2
TC:5 FC:4 - 4.5
TA: 145
CH: 20

According to Leslie's my water is as follows:
PH:7.5
TC: 3.59 FC 1.12
TA: 116
CH: 15
CYA:5
Iron: 0
TDS: 500

I'm mostly concerned with the CC and the CYA. There as been a little "pool smell" after the water was filled, but nothing compared to the "vinyl liner smell" that occurred as I was installing it and before there was water in the pool. The only organics and CYA in the pool are from the tap water, or some mold that was in the piping system (which could have been somewhat significant because I started the project 8 years ago and then got interrupted; and there was some water in the pipes the whole time).

Can I believe the CYA number from Leslie's? At least it was consistent between both of their tests. I haven't tested CYA with my test kits, because the lowest I can test to is 20-30 CYA, and I've got nothing near that. I guess I could see if the solution becomes cloudy at all. If it does, then maybe Leslie's is accurate on that test. Where would the CYA have come from? The town water?

If the CYA was zero, then I've been super chlorinating the water for about 5 days (according to Chemgeek's posts), so that should have burned off all the CC's, right? Unless more are still accumulating from the pipes or lodged in the filter. Still, the 1/2 life of organic matter is supposed to be measured in seconds to minutes in the face of superchlorination. Even if the CYA is 5, as Leslie's suggest, I still think I'm close to the superchlorination level.

The pool is covered and indoors. Under those conditions, how long will CC's take to dissipate or be destroyed under a normal 0.5 - 1ppm chlorine level? I don't think the organic waste load will normally be very high, but it is an swim current machine, so there will be some sweat waste (strange to think of sweating under water).

I know some people use MPS as a non-chlorine alternate for indoor pools, but I'm not really excited to use it, as the chemistry is somewhat mysterious, and I'd like to keep things simple.

Thoughts on the above, especially the CYA and source/longevity of the CC's would be much appreciated.
 

Mdragger88

Bronze Supporter
Jun 1, 2018
1,759
Hernando, Ms
Pool Size
26000
Surface
Vinyl
Chlorine
Salt Water Generator
SWG Type
Intex Krystal Clear
Ignore the Leslie’s test- go w/ the Taylor or tf100 results
Tap water has no cya so u have none if the only chlorine product u have added is liquid chlorine
You may want to add some cya in the future for 2 reasons
1: reduce the harshness of the chlorine on people & equipment
2: it allows you to maintain a reasonable level of fc with some wiggle room instead of trying to maintain 2ppm fc. & your pool being unuseable during a SLAM Process

did u perform the cc test or are you just subtracting the difference between the fas/dpd fc test & the oto test?

From now on steer clear of the pool store & their “free tests”
* going forward get some muriatic acid to lower ph as dry acid has sulfates which aren’t good for your heater (which I’m assuming u have)
* your ch is fine- the only reason to add is if you experience foaming then u can take it up to 150
* You need to do an ahhsome purge to remove biofilms/ nasties in the plumbing. You may need to do several. You don’t have to drain each time. Just after you’re done. This may very well get your cc’s under control. Especially since this sat for so long.
After this you can just leave the cover off & let the water “breathe” after every use for 30min to an hour so cc’s can escape - this is also better for your cover.
I would treat this as a spa & follow this guide 👇
 

JamesW

TFP Expert
Mar 2, 2011
23,144
For an indoor pool, a UV system can sometimes be helpful.

If you are dealing with CCs that you want to be able to get rid of quickly, consider a UV system that you can turn on as needed.
 
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dstutto

Member
Feb 25, 2021
19
NY
Pool Size
3000
Surface
Vinyl
Chlorine
Liquid Chlorine
Mdragger, Thanks for all the info. I will ignore Leslie's and assume I have zero CYA. I'll probably put some CYA in it in the future, but for now I like having the full effect of the CL available and able to shock at lower TC amounts.

The CC was determined with the TF100 kit and Testing the FC and CC by titration. The CC was between 0.5 and 1.0. FC was 3.5 - 4.0 but I called it 4.

I heat the pool using radiant pex floor lines installed in the concrete under the pool. I'm still not wild about Sulfates, so I'll go to Muriatic after this 3lb bag is gone. Dry acid is a little less scary than liquid, but I'm sure once I use it I'll get over my hesitancy.

I'm not ready to purge the pool, b/c it 3k gallons, and I'd have to deal with the liner coming loose/reinstall/ cold water.

I'll check out the chlorine/spa article. Thanks.
 
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dstutto

Member
Feb 25, 2021
19
NY
Pool Size
3000
Surface
Vinyl
Chlorine
Liquid Chlorine
James, Yes, I was thinking about a UV light, and planning to research on TFP for ideas/suggestions/ concerns. My first problem is that I think I will need to replace my pool pump and maybe filter with a smaller pump that pumps more slowly for longer periods. Right now my 1hp pump consumes 1kw/hr and runs for 8hrs/day (about $2/day, which seems high). I think it runs at about 30-50gpm. My predator 50gpm (50 something or other) cartridge filter only shows 5psi resistance. That flow rate would probably make any UV light ineffective b/c the water velocity is too high. I'm not sure If I can keep the old filter and just replace the pump? Does the filter need a certain about of pressure on it in order to capture particles?

My pool turnover at 8hr * 30 gpm would be almost 5x per day. Do you know how low a turnover rate can go and how slow the velocity of water for a small UV light system would need to be? I guess I could always consider a diverter to slow down the water going through the UV light, but then the UV is only "treating" a fraction of the water turnover, which seem counter productive.

My other question is about how long the UV lights last. I believe they degrade over time (14,000 hrs bulb life supposedly from what I've seen), so is it wise to buy a device that's oversized, so that it's more effective over a longer period. When the lights degrades/burns out, can the light itself be replaced or does the whole thing need to be replaced? What is the cost of a bulb replacement? Do the UV lights damage the PVC pipes? I'm guessing the answer is no.

Thanks for your ideas and help.
 
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Mdragger88

Bronze Supporter
Jun 1, 2018
1,759
Hernando, Ms
Pool Size
26000
Surface
Vinyl
Chlorine
Salt Water Generator
SWG Type
Intex Krystal Clear
Ahhsome also has another product called serum that may help u over time- you add it once a week - no draining required.
As well as a pool product that’s similar. I have no experience w/ these but you have a kind of unique situation so just wanted to let u know what’s out there.
James brings up a good point about uv - it has it’s place & your set up sounds like a good match for it. He can guide u on that path.
As far as cya is concerned- it buffers the chlorine so you’re actual active chlorine amount its much lower with it if you’re worried about that
Here’s the original fc/cya chart
See notes 1 & 2