Spas and Ca hardness

Jump to latest Follow Reply
M

Matt

0
Jun 4, 2008
126
We added some Ca hardness from the pool store to a spa. After 2 weeks, it just sat in the pool completely undissolved. It also managed to get into every filter, jet, etc. The spa has been just emptied and refilled... is there something we are doing wrong in the addition of Ca hardness? Is there a better way to do it, or do I need a different form of the chemical from the store?

(It's little round spheres, almost perfectly round, about 1/8 of an inch in diameter, white in color.) It's the same chemical as the spa version, but I'm wondering if the spa version is generally in smaller pieces, and hence dissolves more easily.
 
I suspect that you added too much to the spa so over-saturated the water with calcium carbonate. You generally don't add any calcium to the spa at all as usually the fill water has some and most spas don't have plaster/gunite surfaces to protect.
 
Ok, in that case I'll be happy to ignore the Ca hardness.

I find it's hard to get a good measure anyways, as the Taylor kit never gives me a clear color change. I always get some kind of suspended blue precipitate in a red solution.

The spa is fiberglass, so I don't imagine it's too critical to get the Ca hardness right.
 
Matt said:
Ok, in that case I'll be happy to ignore the Ca hardness.

I find it's hard to get a good measure anyways, as the Taylor kit never gives me a clear color change. I always get some kind of suspended blue precipitate in a red solution.

The spa is fiberglass, so I don't imagine it's too critical to get the Ca hardness right.
Click to expand...
The main reason you need hardness (calcium) in a spa is to help prevent foaming. Soft water foams more readily than hard water and the higher bather to water ratio and aeration from the jets makes foaming a problem in spas. You want your calcium hardness at least 150 ppm.
As for the test... many people have problems with this test. A few things that will help:
be sure to swirl the vial 20-30 seconds between each drop of titrant. Even better, get a magnetic stirrer and use that. This will minimize the purple precitpitate that can form (called a 'floating endpoint")
Often the floating endpoint is cause by interference from other metal ions in the water. This can be minimized by adding 6 drops of titrant to your sample FIRST, then adding the 20 drops of calcium buffer ( actually sodium hydroxide to raise the pH so the magnesium hardness is 'taken out') be sure to swirl well after adding the calcium buffer solution. Then add your 5 drops of indicator and then complete the titration. You do count the first 6 drops in your total, btw.
 
That makes sense, as I know people add borax (water softener) to water when it doesn't foam well to help make more suds in doing laundry etc.

I've tried everything with that CH test and I just honestly cannot get reliable results with it (I can't pin down the color change to more than +/- 5-10 drops sometimes, or 50-100 ppm). I think I may even get better results using strips (which I generally hate). So far I've ignored it, as I have a vinyl liner pool so it just doesn't matter for that. (Foaming in a pool is not such a big issue.) I have seen some foaming in the spa.

You mention that metal ions can cause this problem. Maybe I actually have high levels of metals in my water? I suppose I could treat it with a sequestrant beforehand (like a few drops in a cup of water before testing). I wonder if that would work?

What is spa defoamer anyways?
 
Most defoamers are just simethicone. My feeling on defoamers and clarifiers is that they mask water balance problems and you would be better served to fix the water balance issue. As an analogy, say your dog makes a 'mess' on the rug. You can clean up the mess and solve the problem or you can just spray it with deoderizer so it doesn't smell. However, the mess is STILL sitting on your rug!

As to the calcium hardness test, the titrant is EDTA which IS a chelating agent (this is actually a chelation test. The indicator changes color when all metals--in theory only calcium will be present-- have been chelated). That is why I said to add 6 drops before the calcium buffer, which is just NaOH and will precitptate out the magnesium so only calcium is left. However, if there are other metals they can interfere with the test results. Swirling 20-30 seconds between each drop of titrant is important in getting a distinct enpoint. A magnetic stirrer is even better! (that's what I use). With a magnetic stirrer you can titrate MUCH faster and the endpoint is more distinct. If you calcium levels are high you can also do a low resolution test with a 10 ml sample, 10 drops of NaOH, 3 drops of indicator, and then each drop of titrant is equivalent to 25 ppm calcium hardness. If you are getting a floating endpoint with the smaller sample then add two drops of titrant before the NaoH and count them in your final drop count.

BTW, adding borates to 30-50 ppm to a pool or spa can help stabilize pH by introducing a seconday borate/boric acid buffer into the water. There is a sticky on that you might want to read.
 
I've read about that, but two things about borates concern me.

If I keep adding borates to raise pH, I'm concerned my TDS will increase too much, forcing an early drain/refill of the pool.

Second, I like to keep my pH on the lower end (7.2-7.4) in the pool (not the spa) because it is Cl based and Cl is a much more effective disinfectant at lower pH (more HOCl and less OCl-). Borates will tend to force it higher.
 
TDS is not an important number. It doesn't really matter what the total dissolved solids level is. There are a couple of specific levels that matter. While it is sometimes possible to use TDS as a proxy for those levels, it is simpler to test for the things that make a big difference directly and ignore TDS.
 
Are you suggesting that you can continuously add borates indefinitely? What if your borate level hit 5000ppm? (Not impossible if your pool trends down in pH and you are always raising...)
 
It is very difficult to get the borate level significantly high when using borates to control PH. In almost all pools there is enough water replacement to keep the borate level below 10 forever, even when using borates to counter PH which is constantly falling. Raising borates from 0 to 50 in 20,000 gallons takes over 73 lbs of borax. I can't imagine using that much borax for PH control even over several seasons. Getting the borate level up to 5000 ppm would take over 1,500 boxes of borax and zero water replacement. Technically that is not impossible, but I am willing to say that in practice it is impossible.

By the by, if your PH is constantly falling it is probably because you are using trichlor and/or dichlor for chlorine. When using dichlor/trichlor it is better to use soda ash for PH control, because that is more likely to keep the TA stable than borax is.
 

Enjoying this content?

Support TFP with a donation.

Give Support
I use a SWG, and actually my pH, as expected, constantly increases, so I find myself usually adding muriatic acid to bring it down. Sometimes I add baking soda. I think I added soda ash maybe once ever.

I was more curious about the potential for borate accumulation in the water in general. I doubt it would be a big issue for me in my pool.

I do think though that the borax would fight against my lower pH preferences.
 
Matt said:
Are you suggesting that you can continuously add borates indefinitely? What if your borate level hit 5000ppm? (Not impossible if your pool trends down in pH and you are always raising...)
Click to expand...
You obviously did not read the sticky on borates. You raise them to 50 ppm (and add acid at the same time) to create a borate/boric acid buffer. This works in conjunction with the carbonae buffer to help decrease both acid demand and chlorine demand because of the algaestatic effect of the borates. Borate levels will not keep increasing any more than your salt levels will keep increasing. It will actually go down very slowly just like your salt and CYA from splashout, etc.
As far as running a lower pH to increase the ratio of hypochloruous acid to hypochlorite ion, well that works fine in an unstabilized pool but as soon as you introduce CYA into the equation it all changes and the effects of pH become far less.
Check out the stickies and read the one on water balance for SWGs and then the one on borates.
 
So in a nutshell use bleach as a sanitizer and shock, baking soda to raise total alkalinity, washing soda to raise BOTH pH and total alkalinity when BOTH are too low, and borax to raise pH when the Total alkalinity is correct.
Click to expand...

I did read it actually, and the above quote implied to me that you add borates on an ongoing basis if your TA is fine and you need to increase pH. If your pool continually trends down in pH, that seems like it could be a lot of borax, and that was my concern. Buffers help to lock pH into a range, but after a point, they will all fail, and you end up going out of that range. Even running as low as I do my pH creep is quite noticeable.

I usually keep about 20-30 ppm CYA in my pool and I run my SWG at 10-30% during the daytime, depending on how sunny it is. I keep pH between 7.2 and 7.6. When it hits 7.6, or maybe 7.5, I add acid to drop it to 7.2 and wait for it to start climbing again.
 
Matt said:
So in a nutshell use bleach as a sanitizer and shock, baking soda to raise total alkalinity, washing soda to raise BOTH pH and total alkalinity when BOTH are too low, and borax to raise pH when the Total alkalinity is correct.
Click to expand...

I did read it actually, and the above quote implied to me that you add borates on an ongoing basis if your TA is fine and you need to increase pH. If your pool continually trends down in pH, that seems like it could be a lot of borax, and that was my concern. Buffers help to lock pH into a range, but after a point, they will all fail, and you end up going out of that range. Even running as low as I do my pH creep is quite noticeable.

I usually keep about 20-30 ppm CYA in my pool and I run my SWG at 10-30% during the daytime, depending on how sunny it is. I keep pH between 7.2 and 7.6. When it hits 7.6, or maybe 7.5, I add acid to drop it to 7.2 and wait for it to start climbing again.
Click to expand...
That is not the borate sticky! Try this one! You might want to take some time to read through all the stickies. I think it will clear up some misconceptions you have. You might also want to read this stickyon water balance for SWGs and you might find that you are doing some things that are working against maintaining stable pH and actually creating a higher acid demand then if you follow the guidelines in the sticky. Since you are a chemist I am sure you will readily understand the principles outlines inthe sticky.
 
You must log in or register to reply here.
Thread Status
Hello , This thread has been inactive for over 60 days. New postings here are unlikely to be seen or responded to by other members. For better visibility, consider Starting A New Thread.
Top Bottom
Back
Jump to latest Follow Reply