Calcium deposits?

[halefmly]

Is this a calcium deposit? (see attached photo).
http://pg.photos.yahoo.com/ph/asil22039/detail?.dir=15dfscd&.dnm=c738scd.jpg&.src=ph
Before I was introduced to this site, I used Cal Hypo to deal with an algae problem. I have since been testing regularly, keeping chlorine levels up with my SWCG and pH and alk balanced with muriatic acid. I have had the pool open for 10 months, and had some growing pains with the SWCG, but seem to have a good balance now.

My numbers this morning were:
FC: 9.0
CC: 0.5
TC: 9.5
pH: 8.2
Alk: 130 (I have since added 1 gal muriatic acid-will retest in a couple hours)
Cal: 420
Cya: 60
Temp: 78
Salt: 3200

My typical readings throughout August were:
FC: 8.0
CC: 0.5
pH: 7.8
Alk: 100
Cal: 420
Cya: 65
Temp: 83
Salt: 3200

Can anyone tell me just what the build-up is (in the photo) and how I should remove it?

Thanks,
Larry

[dawndenise]

Hi Larry,

I was hoping to see someone else respond to this so they could better explain the actual chemicals that are in your deposits...there's an explanation for what you're seeing...efflourescence???

Anyway, I have the same deposits that form underneath my rock waterfall and seem to come down the grout lines, although they do exist on the tile, as well. A dilute solution of muriatic acid, about 1 part muriatic acid to 4-5 parts water sprayed onto the surface and then brushed with a hand brush seems to do the trick for me. The stuff will fizz and bubble on the surface as it's clearing up the deposits. Easy to rinse off with pool water right after working in an area, too. When you're done, you can dump the excess solution (shouldn't be much) into the pool where it will work to lower your pH. When working with even a dilute mixture of muriatic acid, I wear rubber gloves and eye protection...quite the site in the pool :eek:.

I've only had my pool 3 months, SWCG about 1 month, and it seems as if I have fewer deposits if I really keep an eye on my pH. My pool's happy at 7.5. When my pool was first filled and the pH was over 8.2, the deposits built up right away, within that first week. Even at 7.8 or just below, the deposits came up fairly quickly. Now, at 7.5, it's several weeks before I feel I have to clean them off.

[chem geek]

Larry,

The deposits may be calcium carbonate because the combination of high CH, high TA, and high pH can lead to this scaling. Your typical readings through August had a saturation index of about 0.5 which isn't extraordinarily high (most people don't see cloudiness until 0.7 or 1.0), however your "this morning" numbers had a saturation index close to 1.0. I would have thought that the water would have become cloudy before you saw such deposits, but perhaps the evaporation of the water above the water line made the concentration much higher thus precipitating calcium carbonate.

As Sandy suggested, dilute acid will dissolve this scale. You should try and keep your pH down closer to 7.5 though you may have trouble doing this with your TA level at 130. If you find your pH rises frequently and you are always adding acid to lower it, then try lowering your TA level significantly down to 80 or below (using Ben's Lowering Your Alkalinity (http://www.poolforum.com/pf2/showthread.php?t=191) procedure) and see if this improves your rising pH and required acid addition. See this thread (http://www.poolforum.com/pf2/showthread.php?t=5379) for more detailed info about possible sources of rising pH in SWCG pools.

Richard

[halefmly]

Sandy and Richard,

Thank you both for the replies. I will use your suggestions to get the scale removed, and also to get the TA reduced.

I have been reading the thread with Ben's method for reducing TA. I have a spillover from the spa into the pool, and also a fountain water feature in the spa. Will those alone create enough bubble action for the outgassing, or should I run the spa's air pump as well?

Larry

[chem geek]

Larry,

For fastest results, run the spa's air pump. The more aeration the better, unless you want to wait longer for the pH to rise (and TA to drop when you add acid). You should also make sure you get good mixing between your spa and pool water -- otherwise the pH rise, add acid, pH/TA drop process will happen much more in your spa instead of your pool.

Richard

[KurtV]

That looks like, as DawnDenise said, efflorescence. That leaches though (or "flowers" if we want to be true to the root of the word) from the concrete/gunite, as opposed to being deposited by your water. Not much practical difference when it comes to removing it, but all the water chemistry in the world won't prevent it if it is efflorescence.

This is pretty common, as I understand it, on raised bond beams and exposed gunite walls. I get it on the back side of the negative edge, even through the tile.

[chem geek]

Larry,

Both Sandy (dawndenise) and KurtV are right about efflorescence (which is why it's so great to have a forum with multiple answers). Your water chemistry is still on the scaling side, but since you don't have cloudy water this isn't something to worry about, though as I said, lowering your TA should help lower your pH rise and acid demand. At any rate, if you make a dilute acid solution using Muriatic acid to clean up the deposits, be sure to remember the rule I learned in chemistry class, "if you're doin' what you oughta, add the acid to the water." The reason is that dilution of acid generates heat so doing it wrong by pouring water into acid can generate enough heat to cause water droplets (with some acid now in it) to boil and splatter (into your face).

Richard

[Simmons99]

Also for maintenance purposes - you probably want to keep your PH closer to 7.4 than 7.8. The SWCG generator will quickly get your PH too high - I try to keep my PH between 7.2-7.4.

[halefmly]

Many thanks to all of you for the advice. I will post here as I make progress against the efflorescence and also the Alk.

Larry

[halefmly]

Well, I needed to use a scraper in conjunction with the acid/water solution, but the efflorescence is now gone. I have been using the aeration method in an attempt to bring down the TA, and it has been hovering around 90 for some time, but today, after a weekend of plenty of pool use and splashing, it is now down to 80.

FC: 14.5 (I have just lowered the SWCG from 45 - 25%)
CC: 0
pH: 7.5
Alk: 80
Cal 470 (that is higher than my usual 420 - I'll recheck)
Cya: 60
temp: 83
Salt: 3000

Thanks to all who have given advice and suggestions in this thread.
Larry

[halefmly]

I just went to the Pool $tore for a replacement bag for my Pentair Pool cleaner, and decided to get a water test. Since the post above, I have kept my Alkalinity down between 80 and 90 for the past two months. (quite a feat with the highly Alkaline water supply in North Texas). Well, the Pool $tore said that I needed to get my Alk up to 100 to prevent "etching the plaster."

Is this real? Should I worry about it? What is the worst thing etched plaster can do?

The Pool $tore numbers are:

FC: 9.4
CC 0.6
TC 10
pH 7.1
Alk 88
TDS 4700
Cya 80
Temp 74
Salt 4000

My numbers with the PS234s:
FC: 11
CC 0
TC 11
pH 7.6
Alk 80
Cal 500
Cya 60
Temp 65
Salt 3600
Do you have any wisdom to share on the Alkalinity and on the variance in the numbers?

[chem geek]

The numbers from your test kit are perfect. The higher calcium hardness compensates for the lower total alkalinity so your water is in perfect balance (and remember that it can get quite a way out of balance before there are problems).

The variation with the pool store numbers that is most distrubing is the pH. The store didn't measure calcium (or at least you didn't show that) and with their measured pH of 7.1 that would indeed indicate corrosive water that could etch or dissolve plaster, though it's still only starting to get out of balance (saturation index of -0.46 though if the pool store assumed a calcium of 300, then the index would be -0.67 which is more worrisome and probably why they made their comment).

Basically, the pH affects the corrosive vs. perfect vs. scaling tendency of your pool water more than any other factor so if your pH is correct (7.6) then you are fine but if the pool store pH measurement is correct (7.1) then you would need to get the pH up. I would trust your numbers over the pool store, but perhaps you could get a cheap separate test for pH just to be sure (perhaps some test strips). If your test kit and cheap test match, then you could let the pool store know about that and see if they can do a similar test with their own water to see if there's something wrong with their pH measurement (might be a meter that uses a pH measurement cell that needs calibration).

Richard

[halefmly]

Richard,
Thanks for the reply. I took your advice and retested my pH with a test strip and again with my drop test. The strip indicated 7.8 and the drop test 7.6.

The store printout did not give me a value for calcium, just Total Dissolved Solids. I think my calcium is so high because I was shocking with CalHypo before I discovered this forum and switched to the simpler method of testing weekly and adjusting only as needed.