First Chemistry Measurements

[sonyak]

We finally moved into our new house and I've had the opportunity to take some measurements of the pool water chemistry with my TF-100.
There are some things that need adjusting, and I'm going to need some help figuring out how to do this.
I'll give you as much information as possible, to make it easier for you to understand the circumstances.

Pool - indoor, fiberglass
Water temp - 86 degrees
Room temp - 89 degrees
SWG has a salt reading of 2.9

Water Readings
10/31/09

FC 5.5
CC 0.5
TC 6
PH 8.2
TA 220
CH 180
CYA 0

1/11/09

FC 2
CC 1
TC 3
PH 8.2
TA 210
CH 180
CYA 0


Yesterday we had 8 people in the pool, so I can understand why my chlorine readings have gone down.
They were high before that because the guys working on the electrical for the pool reset my power, and the SWG ran at 100% for about 36 hours before I rechecked things and discovered the reading was high.
Today I added 2 cups of dry acid (if that's what it's called...), to help bring the PH down. I followed the instructions in the TF-100 blue daily test kit, to figure out how much to add to bring 10,000 gal down to normal readings.
I'm pretty sure all my readings are off and need to be adjusted, but I don't know how to go about doing this.
Any help you can offer would be appreciated.

 

[duraleigh]

Hi, Sonya,

There are much better folks to answer questions on indoor pools than me.......I'm sure they'll be along soon.

Meanwhile, I think you are not too far off in your pool chemistry. With the pump running, your pH should have come down by now (TA as well). Report those two numbers back when you get a chance.

How does your pool water look?

Do you have a stronger "chlorine smell" or not?

My thinking is you need to shock the pool to get the CC's back to .5ppm (and clear up any smell if you have it) or less but I'd rather some of our indoor folks advise you on that.

Once you get your FC and CC's back to around 1-3ppm and .5ppm respectively, then you should search "CYA" and "indoor pools" on this site. I know chemgeek likes to suggest a CYA of about 20ppm but my old brain is having a senior moment so I can't remember why.

 

[chem geek]

The TA is very high and that combined with an SWG is going to have the pH get too high. I'd suggest following the instructions in Lower Total Alkalinity and I'd use Muriatic Acid so that you don't build up sulfates. If you want to reduce fuming from the acid, you could use half-strength 15/16% instead of the full-strength 31.45%, though check prices since sometimes the half-strength is sold for the same price instead of roughly half-price.

The reason for using 20 ppm CYA is to reduce chlorine's effective strength since 2 ppm FC with no CYA is about 5 times stronger than 4 ppm FC with 20 ppm CYA which would normally be recommended (and is still higher than normally found in outdoor pools). This leads to faster oxidation of swimsuits, skin and hair, faster corrosion rates, and potentially greater production of irritating and very smelly nitrogen trichloride. Nevertheless, the rapid rise in CC in this indoor pools indicates that it may have problems with that. See if the CC drops when not having the higher bather load in the pool.

With this SWG pool, the use of 50 ppm Borates is an option to help control the pH, AFTER the TA gets lowered to at least 80 ppm. First see how stable the pH becomes after the TA is lowered and then you can see whether Borates should be used as well.

Richard

 

[sonyak]

There is no chlorine smell in the room, so I'm going to take it as a good thing. All I can smell in there is the freshly installed rubber flooring and the polyurethane that binds it together. I do, however, smell some chlorine on my skin when I'm dried off.

After adding PH- (sodium bisulfate) this morning, I managed to get the PH down to between 7.8 and 7.6.
I don't have any muriatic acid, so I just used what I had on hand. I'll have to go out and get some on Monday.
After reading the article on how to lower TA, I realized that I failed to mention that my spillover spa has been running continuously for the last week or so.
All the heat is running through the spa heat pump until my installers can get the pool and spa heat running separately.
I think this is what I'm supposed to be doing when I get my PH down to the appropriate levels, so aeration shouldn't be an issue. But I'm not really sure I understand how aeration and a lower PH will lower the TA. That's just the "newbie" in me talking...

I'm not sure I understand what CYA is (even after reading the pool school definition of it), nor do I know what I need to purchase to add this to the pool. I've never heard of it before, and when I asked about it at a local "discount" pool supply store, they looked at me like I had 4 heads.

I'm currently experimenting with my SWG to see what % I should be running it at, to maintain the proper levels in the water. Is there an easier way to figure this out? Otherwise, I'll plug along, adjusting it at 5% intervals to see how the water reacts.

 

[polyvue]

But I'm not really sure I understand how aeration and a lower PH will lower the TA.

Acid lowers both pH and TA. Aeration is used to increase pH without also increasing TA.

I'm not sure I understand what CYA is (even after reading the pool school definition of it), nor do I know what I need to purchase to add this to the pool. I've never heard of it before, and when I asked about it at a local "discount" pool supply store, they looked at me like I had 4 heads.

Ha! Better try a different pool supply store! CYA is CYanuric Acid, also known as Pool Conditioner or Chlorine Stablizer. E.g. Leslie's Conditioner Though available as liquid, it's much more economical in dry form (granules). Check ingredient: 100% Cyanuric Acid. If you wanted to add 20 ppm CYA to your 10K gallon pool, you'd need only about 27 oz. That should make a 4 lb. bucket more than sufficient.

I'm currently experimenting with my SWG to see what % I should be running it at, to maintain the proper levels in the water. Is there an easier way to figure this out?

Probably, but I'll bet most people just do what you're doing -- experiment. You're not going to end up with a setting that will always work; depending on bather load and other factors you may have to adjust the % over time.