Calcium Hardness

[Ciscokid]

Hello, I have a 3 year old in ground plaster pool. It is 30000 gallons. I am running a Autopilot dig-220 SWG. My problem is a constantly rising CH.About 1 year ago I had the harness at 600, so I decided to drain the pool and refill. When I was done and got the chemicals back in balance it was down to 200 CH. Now once again I am at 550 CH. Any ideas as to what can be causing this? My fill water is fine. A whole other issue is my constantly rising PH. The only chemicals I add to the pool is Muratic Acid for the PH and occationally I add bleach to get my Chlorine levels where it needs to be. Thanks for any information you can provide me.

[chem geek]

You say you occasionally add bleach to get your chlorine levels where it needs to be, but what is your normal source of chlorine? Are you using Cal-Hypo either in an inline feeder or a floating feeder or adding it manually? Your CH is probably rising due to using Cal-Hypo which for every 1 ppm Free Chlorine (FC) it adds, it also adds 0.7 ppm Calcium Hardness (CH).

Richard

[Ciscokid]

The normal source of Chlorine is coming from the SWG. I use no other chemicals what so ever.

[JohnT]

Well, only two likely causes. One is that you are adding a chemical with calcium. That's out, since you don't. The other is that the calcium is coming from the pool itself. That would be bad. A third option would be that you have a test issue. Have you tried having a pool store test your water to see what they get? I'm concerned that you may be overdoing the acid and dissolving your pool.

[Ciscokid]

That is interesting John.There is one thing I just thought of that might be the source and that would be the salt I added to the pool. I will have to go to home depot where I purchased it and see what other chemicals they may add to the salt.
Now as for it coming from the plaster itself. Is there a way to tell if this is true? Are there tell tail signs? Also should I be concerned with my CH at 550 if it stays there and does not continue to rise? Thanks for your information.

[chem geek]

Sorry I didn't read your post thoroughly the first time -- you had said you had an SWG and I missed that. As for knowing if the calcium is coming from your plaster, the way to know that is to calculate the saturation index for your pool so to do that we need to know the pH, TA, CYA, CH, and water temperature. However, unless your TA and pH are very low, I would be surprised if your water is that corrosive.

For example, with your CH of 200 then if your pH were 7.2 and your TA were 80 and your CYA 70 and temp 80F, then your saturation index would be -0.8 and would probably be corrosive. However, with an SWG it's hard to keep the pH low and in fact you mentioned a frequent battle of rising pH so that implies you probably don't get it much below 7.5 or so anyway.

It's possible that with your frequent acid additions you've gotten the TA so low as to be a problem or that locally acidic conditions dissolved some plaster where you poured it, but why don't you give us the full set of numbers and we can go from there.

The CH level of 550 is nothing to be concerned about, especially if you keep your TA lower to prevent the pH from rising as quickly. By the way, if there WAS corrosion, then this would make the pH and TA rise (whereas outgassing of carbon dioxide makes the pH rise without any change in TA). As for tell-tale signs, it is possible for the plaster to feel more rough and less smooth IF the corrosion were somewhat uneven, but that's speculation on my part.

Richard

[Ciscokid]

My PH is 7.4 TA= 100 CYA=60 and CH=550 Pool temp is 76. Thanks for all the information.
I was also thinking of raising the borates to help with the stabilization of the PH in my pool. I found this in another post.It was very interesting and seems like it will help my situation.

[chem geek]

Well, your saturation index is now +0.06 or essentially perfect. When your CH was at 200, it was -0.32 which is slightly corrosive, but not so much as to cause the CH to rise as you saw it UNLESS the addition of acid kept the pH much lower or the acid pouring corroded the plaster where you poured, but this seems like a stretch. So this is a mystery unless someone figures it out.

Anyway, your pool is in good shape now though you can lower your TA to reduce the tendency of the pH to rise -- with the higher CH you now have, you can lower the TA with no problem (down to 80) using this procedure (http://www.poolforum.com/pf2/showthread.php?t=191) and can also make your pH target around 7.7. This should help reduce the pH rise and certainly the amount of acid you need to add. Adding the Borates will help even more.

Richard

[mas985]

What is your CH of your fill water? You mentioned that you refilled and your CH was 200 which indicates that is all from the fill water. That is fairly high and will build up over time. I have the same problem. When water evaporates it leaves the calcium behind and since the fill water has a fairly high CH, you are continually adding calcium.

[Ciscokid]

What is your CH of your fill water? You mentioned that you refilled and your CH was 200 which indicates that is all from the fill water. That is fairly high and will build up over time. I have the same problem. When water evaporates it leaves the calcium behind and since the fill water has a fairly high CH, you are continually adding calcium.


If this is true that would explain exactly what is going on with my CH.I will measure the CH of my Fill water tonight and double check. I am not to far from you. I live in Manteca, CA. So I would expect the fill water to be similar.

[chem geek]

To get from 200 CH with fill water to 550 CH after evaporation and fill, it would take 550/200-1 = 175% of your pool water volume to achieve that. That's an awful lot of evaporation, but perhaps is what is happening in your case. If you have a bucket of water next to your pool, you can see how quickly the water evaporates. Assuming a 4.5 foot average depth for your pool, you would need evaporation of 4.5 * 1.75 = 7.9 feet of evaporation per year or 0.26" per day (actually double that or around 0.5" per day since there isn't much evaporation in the colder months).

Richard

[mas985]

95" is less than what parts of Arizona and Texas experiences over the year so it really depends on where you live. Check out this Link (http://www.grow.arizona.edu/Grow--GrowResources.php?ResourceId=208) for where you live to get an estimate.

I experience about 60" with is a full pool volume over the year so my CH almost doubles over the year.

EDIT: I should modify this some by saying that with a pool cover, you can greatly reduce the amount of water lost and thus the buildup of calcium.

[chem geek]

What a great link! I've bookmarked that one! Thanks.

[ndillon2]

Cisco,
Does your salt cell clog with scale build up? I have the same issues with CH and PH rising quickly. I go through 2-5 gallons of acid per week just to keep the PH down around 7.2-7.5. The SWG cell clogs with scale every day. I have to remove and clean with a power washer. MY Ch is also 600+ and there are scale flakes that come out of the return lines into the pool. I have considered bypasing the SWG as it is more problem than normal maitenance. However, I just feel like I am missing something and should not give up on it. Any help is appreciated. Thanks

[Ciscokid]

ndillion2,
I don't have a problem with scaling on the Cell.( other than the normal build up.) I clean it maybe once a month or so. Other than my CH being 550 all other chemicals are perfect. The pool itself is crystal clear.
Post all your chemical readings and maybe someone can better help with your problem.
Based on all the help I am going to raise my borates to see if it will slow my PH rise.Also I may airate the pool and get the TA down to 80. Thank you all for you information .

[chem geek]

ndillon2,

It sounds like your've not only got high CH, but also high pH and TA and that combination will often lead to scaling. The solution is most likely to lower your TA significantly. If you post your numbers (including FC, CYA and temp) we can see if this is what is happening and propose a solution.

Richard

[ndillon2]

I tested with a drop kit and strips
FC is currently zero as the SWG has been clogged, not producing. I bypassed it yesterday and supplemented with bleach. I will continue until the cell is replaced
PH = 7.5 I have been maintaining at that level with approx 1/2 gal acid per day
TA = 80 been fairly steady for last couple of months
cya = 70 (adjusted 3 weeks ago from 40
CH = 1000 (test strip test)
temp = 80-84

I have had this problem for two years, constantly battling the SWG clogging abut every two days. I also have the scale ring around the perimeter on the tile. Assistance appreciated.

[chem geek]

If your Calcium Hardness (CH) were truly only 1000, then with a TA of 80, CYA of 70 and pH of 7.5 (and assuming 3000 ppm salt), your saturation index is only +0.14 which isn't high enough to produce the kind of scaling you are seeing. However, maybe your test strip is not able to measure super-high CH levels. However, you'd probably not see scaling unless your CH was closer to 2000 ppm or more. That would explain your situation.

Do you know the CH level of your fill water? Can you measure that separately and let us know? It would be better if you had a more accurate drop-based test for measuring the CH level especially since it is so high (i.e. a Taylor K-2006 test kit or Leslie's Chlorine FAS-DPD Service Test Kit or for just the CH test, the Taylor K-1770 here (http://www.taylortechnologies.com/products_kitinfo.asp?&MarketID=-1&KitID=2196) where you can use the 10 ml sample so each drop will be 25 ppm). As for what to do, that will depend on your fill water so let's get those results first.

Richard

[ndillon2]

Fill water CH is 200 (test strip)

I tested everything today as follows:
CL = 1
PH = 7.6
CYA = 50 (added stabilizer to bring up to 80)
TA = 80
CH = 1000 (test strip)
CH = 460 (pool store test).

The pool store recommended AllClear Stain and Scale for the hardness
I cleaned the salt cell yesterday and this morning it was fully clogged with scale. Flakes continue to come out of the return lines and congreagte on the step just below the return.

Is it possible that scale has built up on the walls and as it breaks up and is sucked through the filter it then clogs the salt cell?

[waterbear]

There are NO test strips that I know of that measure calcium hardness. They measure TOTAL hardness (magnesium and calcium)!

[waterbear]

95" is less than what parts of Arizona and Texas experiences over the year so it really depends on where you live. Check out this Link (http://www.grow.arizona.edu/Grow--GrowResources.php?ResourceId=208) for where you live to get an estimate.



WOW according to this my pool will lose it's full volume plus about 1 third more over a years time and my hot tub over 3 times it's volume!:eek:

[ndillon2]

You are correct. My strips test Total HArdness (1000+), while the pool store tested Calcium Hardness (460). Thank you for pointing that out. At least I feel A bit better about the results being so different.

[salinda]

WOW according to this my pool will lose it's full volume plus about 1 third more over a years time and my hot tub over 3 times it's volume!:eek:

Hey Waterbear...I live in Northern California and evaporation is always a problem. I am wondering if you use a cover at all. I use those silly solar fish and they do seem to mitigate the evaporation quite a bit.

Jumping in here, my calcium is also high at 520-530. It is actually hard for me to get it to blue with the kit because the water in the tube starts globbing up as I add more reagent. I recently successfully lowered my alk from 130 to 90. My ph is hanging out in the mid 7's right now for much longer than it ever has. I have had high calcium for years now and my plaster is very smooth. I do get flakes from the returns sometimes, but the cleaner sucks those into the filter, except in the spa where I use the PoolBuster to remove them. It actually seems like there are fewer flakes this year than in previous years...

I am keeping an eye on everyone's borate experiences as well, but things look good now so I don't want to mess with the water chemistry too much.

[chem geek]

Salinda,

When you had CH of 525, TA of 130, and the pH was rising and hit 7.7, then your saturation index was around +0.6 so slight scaling was possible. With your current TA of 90 and a pH of 7.5, your saturation index is a much more manageable +0.21.

If you use a non-acidic source of chlorine such as chlorinating liquid or bleach, you can lower your TA even more if you want to, even to 50 ppm, and this should further reduce the tendency of your pool's pH to rise. You'll probably find that something like 70 ppm will be fine.

Think of this as an advantage to having a higher CH pool -- you can have a correspondingly lower TA and have calcium carbonate saturation in balance and be even better off in terms of having less pH rise.

Richard

[salinda]

Richard,

Thank you so much! It was your previous comments on the feasibility of low TA with high CH water that gave me the courage to try to fool with the chemistry. I'm glad I did! I test my water myself, but so does the pool store when I go for a visit. This is a local store that maintains pools on their service with liquid chlorine. They completely concurred and understood Ben's method for lowering TA. It sounds like they use this method too. I am steering friends who are looking for a good pool store to this one from now on! The owner was a little concerned about the TDS of the water, but the CH has changed so little in the 3 years I have owned the pool that I am not really concerned.

I use an swg for chlorine. Are you proposing that I turn that off and switch to bleach? I could probably repeat the lower ph/aerating method and get the TA down even further. If I do the adjustment for stabilizer that others do, I am already there.

Maybe we should move this to a new thread....

[chem geek]

Sorry I didn't see your signature line and notice that you had an SWG. No, you don't need to move away from your SWG -- it's fine. But you can lower your TA a little more to around 70 ppm if you want to. It will lower the pH rise a little bit more. Up to you -- if the pH rise isn't annoying where your pool is at now, then there's no need to change it.

Richard