Do Salt Generators damage limestone/masonary

[chem geek]

That's interesting about the spa. You say it's the same water, but it's elevated in temperature isn't it? That would make it less corrosive and more saturated with calcium carbonate (but then after splash out, I would expect it to cool off and be more corrosive again). What is your Calcium Hardness (CH) level? I saw everything else in your post, but not that (also what is the temperature of your pool and of your spa, typically). Also, if your spa has jets, then I expect that it's pH might be higher than the pool (due to more aeration and therefore more carbon dioxide outgassing) and that also makes the water less corrosive (assuming your pool and spa water aren't thoroughly mixing which I assume they are not since otherwise you couldn't keep elevated spa temperatures for long). Have you ever checked your spa pH separate from your pool pH? Also, have you ever checked your spa's FC separate from your pool FC? Those would be interesting numbers. Though the salt may be a contributing factor, it may be that your pool water chemistry is on the corrosive "edge" to begin with so that salt makes it worse. Perhaps keeping the pool more saturated with calcium carbonate *might* help. Let me know the extra info and we'll see if I'm full of it!

Richard

[craiga]

Richard, yes, it is elevated 18 inches. my calcium hardness level is around 300, my total alkalinity is around 105 (both these nos from pool shop analysis from 18 mos ago). the temp varies greatly with the time of year; right now it is 53 degrees. in the summer, it will be 85-90 deg. i just checked temp in both, and they are both 53. the pool and spa share the same filtration equip, and when the pump is running in its daily routine, the spa is overflowing, mixing spa water with the pool water. The spa has jets, but i just checked the ph in the pool and spa, and they are the same (7.8) as for the FC, i just checked it in both and have none showing up in either spa or pool. This time of year, with the water typically in the 50's, i turn off the generator cell and use a floater with a tablet. water usually stays clear, and i adjust accordingly. i know the generator cell has a definite life span, so i try to conserve its use when i can.

[chem geek]

Well, I'm full of it (apparently). Your numbers look good and the pool is properly saturated with calcium carbonate -- I assumed that your pH would drop to 7.6 when the temperature of your water went up to around 88F in the summer. That is typical -- all else equal, the pH rises when the temperature drops and lowers again when the temperature comes back up.

So I'm not sure why your spa coping isn't getting affected as much as the area around the pool. Being elevated shouldn't matter unless it was sloped so that water wouldn't settle on the coping. Apparently, the frequent evaporation of salt water and later rehydration cycling is part of what wears some kinds of stone. So I am at a loss to explain the difference unless the spa pH is different during the summer when it gets used. This summer, try testing the pH between the spa and pool. With the jets running and aeration occurring (which is most likely when the spa is used and the kids are splashing water out), the spa may have increased pH and a small spillover is likely to not be enough to mix with the pool water (though you said it shares the same filtration equipment -- does that mean it truly is the same water and that the spa isn't heated, or does the water go into the skimmer and bottom drains of the pool and come out not only in the pool, but also the spa (with possible additional heating before it gets into the spa?).

Anyway, I'm sorry for the problem you are having. If anyone else has limestone coping, perhaps they can share their experiences, especially if theirs is 3 years old or older. In any event, if your coping is replaced, it should probably be replaced by something that is resistant to corrosion generally, including resistant to salt water (and may require annual sealing, similar to my cement hardscape and coping).

Richard

[fofa]

Something we learned the hard way. We had our pool renovated 5 years ago. We had limestone used instead of tile/coping. We have been having ongoing problems with the limestone flaking, cracking, etc.
One day talking with a stone dealer (for something else, they did not supply stone for pools) I found out there are different "grades" of limestone. The cheaper grades act as the limestone in our pool (which I have been using tri-chlor pucks, bleach only so far).
Anyway, I am no expert but just thought I would pass that on.

[chem geek]

Something we learned the hard way. We had our pool renovated 5 years ago. We had limestone used instead of tile/coping. We have been having ongoing problems with the limestone flaking, cracking, etc.
One day talking with a stone dealer (for something else, they did not supply stone for pools) I found out there are different "grades" of limestone. The cheaper grades act as the limestone in our pool (which I have been using tri-chlor pucks, bleach only so far).
Anyway, I am no expert but just thought I would pass that on.

So this would indicate that the quality of limestone is a primary factor since your pool is not a salt pool (no SWG). Technically, even non-SWG pools have salt in them, of course, but generally it starts at around 350 ppm (the sodium from the bicarbonate and the chloride from the calcium chloride, plus some more chloride from muriatic acid) but usually stays below 1000 ppm with regular dilution from backwashing.

Just to be sure, do you have a DE or sand filter that you regularly backwash or do you have a cartridge filter and yet manually drain and fill part of your pool water? I'm just trying to get a handle on the salt levels in your pool.

Richard

[craiga]

My un-educated theory? Limestone varies in hardness based on the quarry, hardness of the particular seam being mined, ect. Leuters limestone (which is what my coping is) is from a quarry in Leuters Texas that is known for limestone that is particularly hard. However, limestone is a natural product and therefore somewhat un-predictable. The coping stones around my spa are larger stones than the rest of the pool. My guess is that the larger (spa) stones were mined from a different seam than the rest of the pool. The pool stones were probably mined from a seam that had a stretch of soft stone in it. I probably got that batch of stone that is too soft to be used as coping. For that matter, who knows if the stuff really came from Leuters. The name has become analagous with hard stone and a stone vendor can call any stone Leuters and who would know the difference? Just my therory, but i know that a lot of limestone, for instance the flagstone on my deck, is soft and flakes, and would not be suitable for use as pool coping. So, I am going to have it replaced and will apply the best sealer i can find, but based on what i have learned here, the salt water generator is irelevant as to whether it will detoriorate or not.

[fofa]

Just to be sure, do you have a DE or sand filter that you regularly backwash or do you have a cartridge filter and yet manually drain and fill part of your pool water? I'm just trying to get a handle on the salt levels in your pool.

I have a DE filter and backwash as needed (via pressure readings).

[chem geek]

I have a DE filter and backwash as needed (via pressure readings).

Thanks. So your salt levels in your pool are probably in check and well below 1000 ppm. That would make the quality of the stone the dominant factor in your corrosion. So "craiga's" pool builder shouldn't be using the fact that a pool has salt or an SWG as an excuse for what may be poor quality stone.

Of course, the problem is that there may be times when higher salinity is indeed a problem especially with certain types of stone and yet this whole issue gets muddled as fingers point to whom to blame. And there are other times when not using CYA, with the result being very high disinfecting/oxidizing chlorine levels, may be the primary source of corrosion (a possibility in this thread).

Richard