Would it be a good idea to add a bit of calcium hardness increaser?

[JasonLion]

Topics merged. Please keep everything related to a single project/issue/question together in one place.

The recommended levels are normally all you need to worry about. It is normally only worth calculating the CSI if you are unable to remain within the normal ranges of one or more of the levels (for example high TA or CH fill water). Similarly, keeping track of CSI is not sufficient, you have to pay attention to the recommended levels anyway, even when you are also tracking CSI.

CSI only tells you how your plaster is likely to be affected by the water, but that is far from the only issue that needs to be kept track of. The recommended levels are designed to take care of all of the common issues, not just plaster issues.

Finally, CSI can be a fair bit lower than where you have it now without issues.

 

[three4rd]

Hi JasonLion,

The pool is not in service. It has been closed and covered since October. I know of no reason to account for the change in CH. With the pool water not circulating, I know that I have gotten slightly different readings if I partially pull the cover back (such as I have been doing to add pH decreaser and TA increaser a few times over the past several months) then is the case when I simply reach through the skimmer with my Taylor test tubes. That being said though, my testing does overall support a drop in CH. It was about 210 back in October, then 190-200 by end of November, then 200 again on 12/5, then 180 on 12/8. Perhaps I misinterpreted the color change today. It's just confusing as I mentioned. It seems to change to that quasi purplish / bluish color gradually rather than all at once as is the case when testing the TA. I know chem geek had suggested to me that with continue rain and snow dilution that could lower the CH. I'll test again tomorrow and see what I get.

At any rate, would you suggest adding some pre-dissolved CH increaser?

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I have been mostly focused on calculating CSI every time I test, as my plasterer had told me that this is the final determining factor as to whether or not the pool is in balance. So I guess I have started to operate from the standpoint that the index is ultimately more important than any one individual factor. Now from what you are telling me it appears that this is not the case. I agree that if all individual parameters are in range, there should be no need to worry about SI anyway.

 

[JasonLion]

Adding TA increaser without good circulation can cause local calcium precipitation. Without circulation, water in that area might continue to have lower CH levels than the bulk pool water. This isn't the most likely possibility, but it is difficult to rule out.

If the CH test turns purple, it is called a fading end-point, and can cause false high readings. In most cases, simply mixing the sample for a longer time between drops will take care of it, as the purple will go away eventually with enough mixing. There are also other ways to prevent a fading end-point, including using an electric stirrer while testing, or by performing the test slightly differently (see the extended test kit directions in the further reading section of Pool School).

 

[three4rd]

Whenever I added either TA increaser or pH decreaser to the pool after it was closed, I took a kayak paddle and actually got water circulating as best I could - you could see the water moving in a clockwise manner - for at least 10 minutes or so. I can only assume that this water movement continued in the areas of the pool that were not covered since the cover does not rest on the water surface. Anyway, I felt it was the best agitation I could accomplish without the filter and system running. I'm confused about what you are saying relative to the CH test. I read about fading endpoints and understand that. The initial color of the CH test IS purple, and then you look for it to turn to blue. The problem I'm having is knowing after how many drops I can effectively and accurately say that the change to blue has indeed occurred. It seems more of a gradual transition (purplish to lighter purplish to eventually - after about 16 drops - to basically a blue color. All this being said, would you advise adding some CH increaser, being that the level is below recommended range anyway. I'd much rather add that stuff when the pool is in service and I can follow up the addition with good brushing. I've been going mostly by the SI index since that is what my plasterer told me to focus on as the key factor in whether or not to make individual adjustments. I just figured the closer to zero I can keep it the better off I am.

Let me ask this....if the CH level is significantly low, can the water take calcium out of the plaster, i.e. 'etch', even though the SI index indicates that an overall etching condition does not exist? If answer is yes, than the SI number appears to not mean squat and I'd better get in gear with the CH increaser. If answer is no, then I can get a good night's sleep and leave the numbers where they are. Duraleigh suggested that the pH is not at an acceptable level at the current 8, and yet if I drop it and put a lower pH reading into the SI calculator, the overall index then DOES go much farther into the negative zone. This is all driving me nuts....

 

[JasonLion]

Color names aren't the most precise things. The "purple" I am talking about is not the same color as the one the test starts out as. I call the starting color "pink". The actual colors you see can vary from pool to pool somewhat, but regardless "pink" and "purple" are always fairly distinct from each other.

The rule with the test is to keep adding drops as long as the color continues changing. The final drop, the first one which does not change the color any further, does not count.

It is quite unlikely that you want to add calcium while the pool is closed, and you certainly don't want to do so until the test ambiguity is resolved.

 

[three4rd]

That being the case, then either 16 or 17 would be the endpoint. I think I need to test again. But there is no way that I'd get to 21 drops before final color change as I was back near the end of the swimming season. Is there validity to chem geek's assessment that snow melt and rain can account for CH drop?

 

[JasonLion]

Some. If calcium free water is added to the pool and no water is removed, the CH level will go down. But it would require a large increase in the total amount of water to cause the decrease in CH you saw. A 20% decrease in the CH level requires adding 25% of new calcium free water. That seem exceedingly unlikely. Rain and snow melt is something that can have a significant effect, but normally only over months, not weeks.

 

[three4rd]

I'll retest the CH, but I do not think it is over 200 anymore. At any rate, I believe I found an answer to the question I posed in post 24. In the "deep end" part of the forum, I came across a thread dealing with the accuracy of CSI even if one particular parameter is off the recommended range. Here I copied in a post that basically deals with my question and an experiment that answers it.

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When calculating the Saturation Index (SI), does a single low water parameter such as calcium hardness (CH), or a low carbonate alkalinity (C-ALK), make the water automatically aggressive to pool plaster, even when other water parameters are high enough to balance the SI?

To answer that question, an experiment was conducted. Two quality pool plaster coupons were made and cured in balanced water for 90 days. At that point, plaster coupon #1 was placed into SI balanced water, but with a low CH of 90 ppm. The C-ALK was maintained at 110 ppm and the pH from 7.9 to 8.2, which off-sets the low CH and achieves a balanced SI of -0.1 to +0.2.
Coupon #2 was also placed into SI balanced water that had only 45 ppm of C-ALK. The CH of this water was 360 ppm and the pH was maintained between 7.7 and 8.0, off-setting the low C-ALK and achieving a balanced SI of -0.1 to +0.2.

After six months in the water, the coupons were removed, and the water they were in was tested for the calcium content to determine if any dissolution or etching of plaster surface material occurred. Of course, any increase in calcium from the submersion water starting point would indicate that calcium had been dissolved from the coupon, which was the only available source of additional calcium.

The result? There was no increase of calcium in either water container.

Therefore, these results indicate that if the calcium hardness or the carbonate alkalinity is low, but the water is still determined to be SI balanced, the water is not aggressive. This indicates that the SI is applicable for plaster swimming pools.

This experiment was conducted because some in the pool industry claim that pool water with a low CH or a low C-ALK is automatically aggressive despite what the SI actually is. Often, when a new pool plaster surface has undergone severe gray mottling, white spotting, streaking discolorations, flaking, nodules, or other defects actually attributable to plastering errors, the finger is pointed at aggressive water chemistry instead. Specifically, a CH or C-ALK below the APSP Ideal minimum is blamed, even in cases where the actual LSI is balanced.

It is interesting to note that the current National Plasterers Council (NPC) 7th Edition Technical Manual states that if any isolated, individual water parameter (pH, C-ALK, or CH) is lower than the Ideal range as defined by the APSP, the water is aggressive. Therefore, the NPC is (incorrectly) stating that when the C-ALK is less than 80 ppm (while the total alkalinity may be above 80 ppm), or when the CH is less than 200 ppm, or when the pH is below 7.4, (which are the lower ends of the APSP Ideal Standard), the water is automatically aggressive and considered to be detrimental to the plaster finish (even though the SI may be balanced).

This is a complete departure from the NPC text on this topic in their 5th Edition of the Tech Manual. It stated that pool water needed to be within the acceptable tolerance range as established by the APSP, which set the “minimum” for C-ALK at 60 ppm, CH at 150 ppm, and a pH of 7.2. It is apparent that the water balance requirement by the NPC is more restrictive now. Why did the NPC make that change? Where is the study documenting that a low CH or C-ALK is automatically aggressive when the LSI is 0.0 or higher? Has the National Pool Industry Research Center at Cal Poly (NPIRC) proved that? No.

Now, we are not necessarily promoting the concept that pool water should be maintained on a regular basis with the pH, C-ALK or CH below the minimum APSP targets. We are not even suggesting that the ranges below the ideal are always the optimum. We would recommend that pH and C-ALK levels be maintained above the ideals, not below, whenever possible. However, we understand two things: that there are times when lower pH, CH or C-ALK are unavoidable, and when that chemistry is SI balanced, it means exactly that, it is not a tool for blaming plaster defects on water chemistry.

As the above plaster study demonstrated, pool water with a single low water parameter (even below the APSP Ideal or Minimum standard) can be non-aggressive if the SI is balanced.

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Based on the above, it would appear that I can continue to rely on the SI until conditions are more appropriate for adding calcium to bring up the CH level (like when the pool is open and water circulating). Hopefully, next winter I won't have to be as concerned about any of this since the curing process of the new plaster will be done.

 

[JasonLion]

Let me ask this....if the CH level is significantly low, can the water take calcium out of the plaster, i.e. 'etch', even though the SI index indicates that an overall etching condition does not exist? If answer is yes, than the SI number appears to not mean squat and I'd better get in gear with the CH increaser. If answer is no, then I can get a good night's sleep and leave the numbers where they are. Duraleigh suggested that the pH is not at an acceptable level at the current 8, and yet if I drop it and put a lower pH reading into the SI calculator, the overall index then DOES go much farther into the negative zone. This is all driving me nuts....

You are trying too hard. You don't need to get things as fine tuned as you seem to be trying for, let alone maintain them that way frequently while winterized. I am going to go ahead and answer some of your more technical questions below, but really you just need to relax and let things be.

So, you should ignore this, but:

If you know the SI at every instant, which you don't, but if you did and it stayed around -0.2 to -0.3 then you would not have any detectable plaster etching. But plaster etching isn't the only issue, and things can change even when you don't expect them to.

High PH increases your risk of metal staining. That isn't a problem if there aren't any metals in the water, but then you never really know if there are metals or not, as the tests are not especially reliable. PH being a little high also limits your ability to track the PH going up. Since the usual PH test reports anything above 8.2 as 8.2, you need to keep the PH below 8.2 least you have no idea how high the PH has gone. With PH starting at 8.0, you are very very close to hitting that ceiling, which makes managing the situation more complex and gives you less room for mistakes.

Getting back on topic:

With plaster only a few months old (or less), then the risk over the winter is PH, TA, and CH all going up due to ongoing plaster curing, resulting in calcium scaling. That doesn't seem to be what is happening, so your risk is very very low. With plaster applied in the late fall it is worth testing over the winter about once a month to watch for PH, TA, and CH all going up. Don't bother with worrying, or adjusting anything, unless at least one of those goes up significantly.

Since you are expecting CH to go up, if not now, then eventually, and the pool is winterized, I wouldn't worry about CH being a little low until you open the pool. However, you should open the pool as early as possible in the spring, since warmer temperatures will bring PH, TA and CH increases.

 

[duraleigh]

I'm confused. You refer to CSI as being rather unimportant.

Absolutely. In most all pools, yours included, keeping the pH, FC, etc. all within the guidelines suggested is all that's needed to manage your pool.

Far too often, I see relative newbies anguish over CSI............there is virtually no reason unless your basic parameters of pH, TA and CH get outside of normal.

 

[three4rd]

Thanks much guys. I appreciate it. I'm actually not a newbie - having had the pool for 25 years, but recently replastered. I am fairly new to this site though. It's been very helpful. Over the years I really never paid much attention to the SI at all before. I took the pool store advice, bought whatever they suggested and went from there. I now like doing my own testing. I know I've been over-testing and overly concerned. It's been 25 years since I went through the whole new plaster / high pH routine. I really don't recall even being that concerned about it during the first winter after I had my pool put in (but then I probably don't remember alot of it either).

I looked back at my pool (store) test history over the past many years and found that my CH was basically always a bit low. I can recall always having to add increaser both at the beginning and end of the season. I can't account for why it always tended to stay on the low side. Here are the numbers I've had -

6/8/04 141
9/18/04 139
6/10/05 122
6/23/05 179
6/9/06 264
9/30/06 186
6/14/07 135
9/15/07 134
6/10/08 128
9/20/08 75
6/10/09 103
9/19/09 170
6/5/10 121
6/13/11 126
9/18/10 154
9/20/11 86
5/29/12 93
9/5/12 151
5/31/13 142
9/14/13 179
7/7/14 199
7/28/14 179 (my result from first time I ever tested myself).....205 (store's test result) This last is interesting. I'm hoping that my test was the more accurate than the store's, which, from things I've read here, such is often the case.

My SI over the years has OFTEN been on the negative side. It's almost amazing that my plaster was still in pretty decent shape after 20 years. We'll see how long the new finish lasts.

Thanks again,
Keith