Questions on Calcium Scaling

[socalsharky]

I have a 15,000 gallon gunite pool with a SWG. The water is about 5 years old (so is the pool) and calcium scaling has progressively gotten worse. For the first 2-3 years, there was little or no calcium scaling at all, with a minor exception of the natural rock at the spa overflow. Now this rock, as well as the rock on the water line in the spa has severe scaling, with minor scaling on the tile around the pool water line. My water clarity is awesome, and I have no algae since I added some phosphate removal product last summer.

I had the water tested this weekend, and the CH is 700 ppm!! In researching the water quality report from our water district, our tap water has a hardness of 250-320 ppm, so I guess after 5 years this is not surprising. It looks like a complete drain and refill is in order. In light of this, I have a few questions:

1. I am constantly battling the pH creep associated with the SWG. Is adding enough acid to bring the pH into the 7.2 to 7.4 range on a weekly basis enough? By the time the next weekend rolls around, the pH is back up to 7.8 or 8.0 which has left the pool vulnerable to scaling. Should I be adding acid every two days or so? Or adding enough to drop it to 7.0 or so, such that the average is more like 7.4 over the whole week?

2. How much will the borates help with this? I have never heard of borates before visiting this site. Is this a widely used technique, or more of a "cult following", for lack or a better term?

3. What about devices, like the mpulse 3000, that purport to change the calicum molecules into a more manageable form? This sounds like a lot of hooey to me, but I'm willing to try it if others have had good success.

4. What is the best method of removing the severe calcium scaling on my rock work? I am thinking of getting a bid for bead blasting this rock (it's natural rock) and then trying to monitor my pH more closely in the future to reduce the scaling. Acid washing will probably handle the scaling on the tile line, right?

Thanks in advance

 

[JasonLion]

Welcome to TFP!

Calcium scaling only occurs if you allow your water to get out of balance. If you have a good test kit and stay on top of your numbers then there won't be any further calcium scaling.

1) We can tell you how to reduce your PH drift, most likely reduce it dramatically. It would be simplest to explain if you post a full set of water test results. Then we can tell you exactly what you would need to change.

2) Borates will help. Using borates to control PH drift is a fairly new thing that I have not see widely used in the pool industry. Quite a number of people here have tried it and it works, but I suppose you could say that it was "on the fringe" or something like that. Using borates in general is quite mainstream, but borates mostly used for other reasons.

3) The mpulse does not work, doesn't help at all.

4) There are not a lot of choices, basically bead blasting or an acid wash.

If you are going to do the full acid wash to remove the scale, you will be replacing all of the water in the pool anyway.

 

[socalsharky]

Welcome to TFP!

Calcium scaling only occurs if you allow your water to get out of balance. If you have a good test kit and stay on top of your numbers then there won't be any further calcium scaling.

1) We can tell you how to reduce your PH drift, most likely reduce it dramatically. It would be simplest to explain if you post a full set of water test results. Then we can tell you exactly what you would need to change.

Current Water Test Results:

FC = 2.0
pH = 8.0 (I added MA after this test result, pH is now 7.4-7.6)
TA = 80
CYA = 30
CH = 700
Salt = 3400

I had planned to add CYA to get to 70ppm, but am holding off on this until I decide whether to drain the pool.

Welcome to TFP!

4) There are not a lot of choices, basically bead blasting or an acid wash.

If you are going to do the full acid wash to remove the scale, you will be replacing all of the water in the pool anyway.

Why would I need to drain the pool after an acid wash? I was under the impression that only the water line (and maybe slightly below it) would require acid washing to remove scale. Is there scale down on the pebble finish, which is 3 to 4 inches below the water line, too? I doesn't look like it to me. It looks as if the sclae formation only occurs where the surfaces are repeatedly wetted and dried.

Thanks again

 

[JasonLion]

I guess I misunderstood you, sorry. If you don't have scale below the water line then there is no need to do a full drain. I thought you had scaling below the water line. Reading over again, I see that you didn't say that.

To slow the rate of PH drift, I suggest lowering the TA down to around 60, or perhaps even 50. This will also reduce the amount of calcium scaling somewhat.

When dealing with high CH levels in your fill water it is important to keep an eye on your CH level and reduce your maximum allowed PH and your TA level as the CH level rises. It is possible to continue operating with CH around 700 if you can get TA down to between 50 and 60 and be certain that PH will never go above 7.6.

By keeping the PH and TA under control you can greatly slow the rate of scaling on stone above the water line, but not eliminate it. Water that evaporates off the rock will leave the calcium it contains behind. Lowering the PH and TA will help subsequent water that splashes on the rock and runs off to carry away some of the calcium, but some will always stay behind.

 

[socalsharky]

Jason--Thanks so much for your input. A few more questions/clarifications:

Would you recommend a drain and refill? It seems as though that would greatly reduce the potential for scaling.

Could you address my previous question about how to add the acid?

Should I consider the borates?

I have always been told that TA was a pH buffer. It would therefore seem that lowering the TA would increase the pH drift?

Thanks again, Greg

 

[JasonLion]

With high CH levels in your fill water, you are going to need to drain and refill at some point. Depending on how expensive water is and how good you are at making sure the PH never goes above 7.6, it might be better to do that now or it might be better to put it off for another year.

You need to add acid frequently enough to keep the PH from getting too high. How frequently that is depends on your rate of PH drift. You can add enough acid to get your PH down to 7.2 or to 7.5. Adding acid down to 7.2 gives you a little more time, though not as much as you might think, between acid additions, but causes the TA to need to be adjusted more frequently. Lowering PH down to 7.5 uses less total acid and requires less TA adjustment, but means slightly more frequent acid additions.

Borates will help reduce the rate at which the PH rises. Borates will not reduce the scaling, except indirectly by giving you a little more control over your PH. I like borates for a number of other reasons as well, so I recommend trying them.

TA does two different things. Higher TA levels buffer the PH, causing it to change more slowly. At the same time, higher TA levels put upward pressure on the PH, so that it drifts up when there is aeration. Depending on how much aeration you have and what other chemicals you are using, various TA levels may give the most stable PH. Borates also act as a PH buffer, without the upward pressure aspect.