Pool in Arizona . Need help with a couple things...

[spoonman]

Hi folks,

I live in Arizona and we have REALLY hard water. My pool is 18 months old and my CH is already at 1425. I’ve only used liquid chlorine too and it’s still that bad.

To add, my 12,000 gallon pool has always drank muriatic acid like a fish (half gallon min). It has been tough keeping up so I’m adding a Stenner pump for acid.

Im starting to get scaling at the waterline. My belief is this is a combination of the high CH and my difficulty keeping up with the acid (harder as the CH rises).

Does anyone have any feedback on my situation? Do I need to drain? I’m not sure my CSI but I suspect it is tough to keep the calcium at bay since I can only run the pH so low. Any ideas?

My pH yo-yos but my target is 7.4. Alkalinity usually around 40-50.

 

[Texas Splash]

That is a crazy CH level so soon. It sounds as if you understand the relationship of all three (PH, TA, CH) and how they impact your CSI, so now it's really a matter damage control. You've got the TA just about as low as you can go. PH could go a bit lower, but it may drag the TA down as well. A water exchange is probably your best bet to lower the CH a bit. From there perhaps consider supplementing some of the new fill (or perhaps later evaporation refills) with soft water. Some people speak of reverse osmosis, but I'm not sure it's available in your area or worth the trouble. Someone else may add to that issue. Something you might give serious consideration to is a cover if you don't already have one, just to help reduce evaporation to reduce refills with more CH. The bonus is it should reduce FC use as well. Those would be my initial thoughts. Others might expand on an issue I missed.

 

[spoonman]

Thanks Splash. Good ideas. I didn’t think of using a cover to help slow the water loss. Our tap water here in AZ is 400CH if I recall. Not a great place to start, so slowing that could help.

 

[cfherrman]

Your doing good, but it's time for a drain.

I recently installed a water softener for my whole house and to fill the pool, I went with the biggest I could find, $640 for a 64,000 grain (you should get the double tank), my water is ch 250 and this gives me 4000 gallons per a regen, yours would be a little less that half that, but probably the best option for your pool, and cheaper than ruining your plaster and replacing.

 

[duraleigh]

A whole house water softener is your best bet. A cover over the pool would help also.

To get started, I would drain 50% of the pool......that should get your CH down to around 900, which is still too high but, if you get the softener, you can start to reduce it.

Pools in AZ have high CH as a common issue. It's a PITA to have to do these things but, as said above, cheaper than ruining your plaster.

I would also attack that waterline scale ASAP.....it will only get worse the longer it stays on your pool surface.

 

[JoyfulNoise]

Somethings not adding up here. I’m in Tucson and my muni water is about 280ppm CH (CH and GH are different things...many munis report GH). My pool water is currently 1500ppm CH after almost 5 years! So, unless your pool was hit with a lot of Cal-hypo on startup or the plaster was incorrectly started and it leached CH in your pool, going from a new fill around 300ppm to 1400ppm in less than a year would require that your pool water volume evaporated several times over.

Can you be more specific and detailed about what has been done to this pool? How was the plaster started and what chemicals have been added?

 

[spoonman]

My pool is 18 months old. I’ve never used CalHypo. I’m not sure what the PB did at startup. However, I’ve suspected that the PB used calcium? during the plaster process as I’ve had splotchy plaster starting a few weeks after the pool was done. Don’t know if this has any bearing, but the pool has always been thirsty for acid (in my opinion), using 1/2 gallon a week at minimum for 12k gallon pool.

- - - Updated - - -

A whole house water softener is your best bet. A cover over the pool would help also.

To get started, I would drain 50% of the pool......that should get your CH down to around 900, which is still too high but, if you get the softener, you can start to reduce it.

Pools in AZ have high CH as a common issue. It's a PITA to have to do these things but, as said above, cheaper than ruining your plaster.

I would also attack that waterline scale ASAP.....it will only get worse the longer it stays on your pool surface.

What is the best way to attack the scale on the tile? I got a brush and tile cleaner but it doesn’t seem very effective.

 

[JoyfulNoise]

Your target pH of 7.4 is WAY too low. Here in the desert you can’t easily maintain a pH that low and it is why you are using so much acid. You should be targeting a pH of 7.6-7.8 and not lowering your pH until it goes over 7.8. When you adjust pH, you should only add enough acid to get it down to 7.6. As well, you want to keep your TA on the low side, 60-70ppm at most. Finally you want to limit aeration from spas, spillovers, waterfalls etc. Your signature says you have “aerator jets” ? Those should not be running unless someone is using them. Aeration of the water causes pH rise and, with your target at 7.4, you are shooting yourself in the foot.

If you are confident that you are measuring CH correctly, then someone added calcium to the pool at startup or the plaster was improperly started and it leached a lot of calcium into the water (the major component of plaster is calcium oxide and calcium hydroxide). There is no way with fill water at 300ppm CH that you can buildup that much calcium hardness in 18 months. Pan evaporation data in your area would suggest that a fully uncovered pool would lose 90-100” of water per year to evaporation. For your size pool, that’s about it’s entire volume. So the fill water would, at most, increase your CH by 300ppm. Your only way to remediate the CH level us to drain and refill.

For tile cleaning I would personally recommebd you call Mark White at Arizona Bead Blasters and ask him how much his MaxxStrip process is running these days. Kierserite blasting is the best way to clean pool tile without damaging it.

 

[spoonman]

The reason I target my pH lower is that it rises so fast I would be pouring in acid almost daily if I targeted 7.6. Everytime I go check the pool it is back up past 8. It has been a constant battel which is why I'm adding a Stenner pump to dose the pool with acid each day. If I do that I'm sure I could hold at 7.6-7.8.

That said, I have no idea why the pool is sucking up so much acid. I have "aerator jets" but only use them in the summer when the pool is in use. We don't have a spillway or anything like that. Is the very high CH pushing up the Ph?

 

[spoonman]

Somethings not adding up here. I’m in Tucson and my muni water is about 280ppm CH (CH and GH are different things...many munis report GH). My pool water is currently 1500ppm CH after almost 5 years! So, unless your pool was hit with a lot of Cal-hypo on startup or the plaster was incorrectly started and it leached CH in your pool, going from a new fill around 300ppm to 1400ppm in less than a year would require that your pool water volume evaporated several times over.

Can you be more specific and detailed about what has been done to this pool? How was the plaster started and what chemicals have been added?

How are you able to have a CH of 1500, pH up to 7.8, alkalinity of 60-70ppm and not have scaling? That sounds like a recipe for positive CSI as I understand it.

 

[spoonman]

Playing with the pool math calculator, if I can hold pH at 7.6 and TA at 50, I should be able to maintain a CSI of +.27 at 80 degrees and 1425CH. Could probably even let the TA and pH run a tad higher and be OK. The key though would be holding the pH steady which seems an impossible task without a Stenner (or starting to use pucks :-/ )

 

[JoyfulNoise]

The reason I target my pH lower is that it rises so fast I would be pouring in acid almost daily if I targeted 7.6. Everytime I go check the pool it is back up past 8. It has been a constant battel which is why I'm adding a Stenner pump to dose the pool with acid each day. If I do that I'm sure I could hold at 7.6-7.8.

That said, I have no idea why the pool is sucking up so much acid. I have "aerator jets" but only use them in the summer when the pool is in use. We don't have a spillway or anything like that. Is the very high CH pushing up the Ph?

This is a detail that few people get at first but it is a fact of chemistry - when you lower your pH as far as you are going, you actually make your pH rise worse and buy yourself very little "extra time". In other words, the rate of rise in pH is NOT linear - the lower in pH you go, the faster the rise will be. This is because low pH water has a higher saturation limit for dissolved CO2 than does higher pH water. So, when you lower the pH, you increase the rate of outgassing of CO2 and your drive the pH up faster. You really don't want to keep your pH at 7.4 and, with an acid feeder, you'll chew through all of your TA by trying to drive the pH down that far. Then, in order to compensate, you'll be adding baking soda to make up for the lost TA.

CH has no effect on pH. Your high CH is simply a consequence of the water and chemicals added to your pool. As others have suggested, tying a water softener into your fill line will help to keep the CH rise down because your fill water will be low in CH. A water softener can easily get the CH of the municipal water below 50ppm (and in many cases, it will go down to immeasurable levels) and so that will keep the annual rate of CH rise very low.

How are you able to have a CH of 1500, pH up to 7.8, alkalinity of 60-70ppm and not have scaling? That sounds like a recipe for positive CSI as I understand it.

My CH was about 1200-1400ppm all last season and I was easily able to keep my CSI in the negative range by simply lowering my TA target and keeping my pH between 7.6-7.8. But yes, tile scaling does get worse with higher CH. After 4-1/2 years with this fill water, I will be draining and refilling soon. What keeps scale out of my SWG is the fact that I keep my CSI negative AND I use borates in my pool water. Borates act as a high pH buffer and so the pH rise inside my SWG cell when it's running is probably half of what other people experience with no borates. Because I run my SWG at low output and for only short periods of time, I save from cell from developing a lot of scale.

 

[JoyfulNoise]

Playing with the pool math calculator, if I can hold pH at 7.6 and TA at 50, I should be able to maintain a CSI of +.27 at 80 degrees and 1425CH. Could probably even let the TA and pH run a tad higher and be OK. The key though would be holding the pH steady which seems an impossible task without a Stenner (or starting to use pucks :-/ )

Holding it steady is not necessary. My pool would go from a pH of 7.6 to slightly over 7.8 in about 7-10 days. So I would add a little less than a quart of acid every week or so. That's not a very time consuming task and my pool happily stayed scale free. I am of the opinion that an acid dosing tank is overkill for most situations and will simply lead to more trouble than it's worth. A person can swim in a pool with water pH anywhere from the high 6's to mid-8's and never feel any discomfort whatsoever. So there is no reason to target an exact value when holding it to a small range will be perfectly fine. It's certainly up to you and your personal situation, but I can think of a lot better things to spend $400 on than an acid injection tank....

 

[spoonman]

Holding it steady is not necessary. My pool would go from a pH of 7.6 to slightly over 7.8 in about 7-10 days. So I would add a little less than a quart of acid every week or so. That's not a very time consuming task and my pool happily stayed scale free. I am of the opinion that an acid dosing tank is overkill for most situations and will simply lead to more trouble than it's worth. A person can swim in a pool with water pH anywhere from the high 6's to mid-8's and never feel any discomfort whatsoever. So there is no reason to target an exact value when holding it to a small range will be perfectly fine. It's certainly up to you and your personal situation, but I can think of a lot better things to spend $400 on than an acid injection tank....

Actually I originally bought the Stenner to use for liquid chlorine, but I decided to use for acid as it has been harder to keep up with than the CL. My intention is to provide a small dose each day as opposed to having large doses less frequently. Technically there would be a range...lowest after dosing and highest next day prior to dosing...so i wouldn't maintain a specific number around the clock, but I obviously want to control the min/max as much as possible.

You brought up a good point that the TA could plummet with constant dosing if the "target" is too low. I'd think that if the low value was 7.6 or 7.7, whereby I dosed each day, I wouldn't have TA issues like I would trying to achieve a lower value.

 

[cfherrman]

If you don't have water softener I can tell you going from 250 ppm to 0 ppm for a shower or even drinking water is such a night and day difference. My daughter eczema is going away almost completely.

To start to clear a few issues up in the air, can you test your fill water ch?

 

[JoyfulNoise]

The TA level will depend on your fill water input. Your TA will be reduced with every acid dose. If your evaporation and fill doesn’t balance that, then you’ll need to add alkalinity to compensate.

 

[spoonman]

This is a detail that few people get at first but it is a fact of chemistry - when you lower your pH as far as you are going, you actually make your pH rise worse and buy yourself very little "extra time". In other words, the rate of rise in pH is NOT linear - the lower in pH you go, the faster the rise will be. This is because low pH water has a higher saturation limit for dissolved CO2 than does higher pH water. So, when you lower the pH, you increase the rate of outgassing of CO2 and your drive the pH up faster. You really don't want to keep your pH at 7.4 and, with an acid feeder, you'll chew through all of your TA by trying to drive the pH down that far. Then, in order to compensate, you'll be adding baking soda to make up for the lost TA.

This is an interesting concept that I understand to some degree. I've understood that the relationship is not linear, but wan't aware that this could perhaps create momentum to drive the pH up faster overall. For example: Let's say that I would normally lower pH to 7.6 and it takes the water 2 days to go from 7.6 to 8.0. Now, if I dose my pool down to 7.4, I understand that it may jump from 7.4 to 7.6 quickly, but would it still take the same 2 days to go from 7.6 to 8.0, or would this happen faster because of "momentum" created from the speeding up of CO2 offgassing?

 

[JoyfulNoise]

This is an interesting concept that I understand to some degree. I've understood that the relationship is not linear, but wan't aware that this could perhaps create momentum to drive the pH up faster overall. For example: Let's say that I would normally lower pH to 7.6 and it takes the water 2 days to go from 7.6 to 8.0. Now, if I dose my pool down to 7.4, I understand that it may jump from 7.4 to 7.6 quickly, but would it still take the same 2 days to go from 7.6 to 8.0, or would this happen faster because of "momentum" created from the speeding up of CO2 offgassing?

No, that's not an effect you would see. The rate of outgassing is a first-order diffusion problem where the rate of outgassing is proportional to the concentration of dissolved CO2 in the pool water. This chart shows how over-carbonated pool water is relative to atmospheric levels and why the lower you go in pH, the faster the outgassing happens. For example, when the TA is 80ppm and the pH is 7.5 (these are values that are cited as "good" by the industry), you have 8 times as much dissolved CO2 in the pool water as you do in the air above your pool. That is a huge concentration difference.

However, the initial rate of outgassing does not influence the future rate of outgassing, it is solely proportional to the current concentration of CO2. This why outgassing slows down as pH rise - there's less and less CO2 dissolved in water at higher pH and so the outgassing rate slows down. You see this in your pool as a fast initial pH rise from 7.2-7.5 and then, once the pH crosses 7.6 it will stay between 7.6 and 7.8 for a longer time.

 

[spoonman]

Thanks Joyful. That chart is really helpful and does a good job illustrating the uphill battle of trying to hold a low pH. Also shows how great a role TA plays in the equation.

 

[Arizonarob]

The TA level will depend on your fill water input. Your TA will be reduced with every acid dose. If your evaporation and fill doesn’t balance that, then you’ll need to add alkalinity to compensate.

Matt, what causes the TA to fall if there is no aeration? I thought in order to bring TA down, there had to be aeration of the water to introduce CO2?