First-timer doing water chemistry test

[Fedderman]

I have owned a pool and spa for a few years, and delegated all routine maintenance (including water chemistry) to a weekly service. This is a 2nd home, and we were usually here just on weekends before I retired. Now that I am retired and we are spending more time here, I figured I should start paying more attention to the pool, since I have noticed significant “mottling” on the bottom which appears to be scale (pool and spa were replastered ~5 years ago). So, I recently joined TFP, and today I performed my first tests using the TF-Pro test kit. Here are the results for the pool & spa:



I will share these results with the pool service manager, as several things seem to be out of balance; the last service was 2 days ago. It is now dawning on me that even though I used a service, I should have been actively monitoring this myself.

 

[ajw22]

Your pool chemistry looks fine except for the CH which is way high. You need to drain at least 2/3 of your water to get your CH down below 400.

The high CH is why you probably have scale on the surfaces.

Calcium Hardness - Further Reading

www.troublefreepool.com

Calcium Scale - Further Reading

www.troublefreepool.com

Your spa FC is low and the CC of 1 is concerning.

How is the spa chlorinated?

What is the pH, TA, CH of your fill water?

 

[Fedderman]

Your pool chemistry looks fine except for the CH which is way high. You need to drain at least 2/3 of your water to get your CH down below 400.

The high CH is why you probably have scale on the surfaces.

Calcium Hardness - Further Reading

www.troublefreepool.com

Calcium Scale - Further Reading

www.troublefreepool.com

Your spa FC is low and the CC of 1 is concerning.

How is the spa chlorinated?

What is the pH, TA, CH of your fill water?

Thanks for the analysis and references, Allen! The spa had a dead bird in the spa skimmer basket, which I removed a week ago, not sure if that explains the spa FC and CC levels (the pool service 3 days ago *should* have fixed it). The service uses liquid chlorine in the spa (and until ~a month ago, also used a floating chlorine tablet dispenser until it broke, not replaced yet).

Here's the fill water (city water) chemistry, which I just now measured:
pH: 6.8
TA: 60
CH: 50

I'm trying to figure out how the pool CH got so high; it now seems obvious the service was not testing for it. The pool service uses both liquid chlorine and a floating dispenser filled with chlorine tablets in the pool - I now understand that these tablets can introduce both calcium and CYA, so perhaps they shouldn't be used in our pool anymore. I wish there were an easy way to reduce CH without replacing the water.

 

[ajw22]

If the pool service put TriChlor in the floater it added chlorine and CYA.

If the pool Service put Cal-Hyp in the floater it added chlorine and calcium.

No way to reduce CH without draining.

Draining - Further Reading

www.troublefreepool.com

 

[Fedderman]

Thanks! I’m wondering what the process/sequence should be re: scale removal and water replacement. Since the water needs to be replaced, it seems a no-drain acid wash is the wrong way to go… opting instead for draining the pool, then some process to remove the scale, then refill. At this point I’m losing confidence in the pool service company to make the right call. I’ll be asking them today for a proposal. I’m also wondering if there may be scale buildup in the heater.

I attached a pic - some areas on the bottom of our “black bottom” pool are almost completely covered, others near walls are a bit more spotty.

 

[ajw22]

Is the surface smooth or rough to touch?

Any acid wash will reduce the life of the plaster that you care about but your Pool Service does not.

Draining and polishing off the scale using diamond pads is more labor intensive and expensive but will give you a better finish.

 

[Fedderman]

Is the surface smooth or rough to touch?

Any acid wash will reduce the life of the plaster that you care about but your Pool Service does not.

Draining and polishing off the scale using diamond pads is more labor intensive and expensive but will give you a better finish.

I believe the surface is smooth (at least no rougher than the plaster, which has quartz in it). If it’s important, I can brave the cold water and check where it is the worst (on the bottom) with my feet next time I’m there. I’ve seen a few small thin flakes that my pool robot picked up, which were a light brown color.

 

[Fedderman]

Here’s what the pool service manager had to say about the scale:
- The majority of pools in my area have a high CH (concentrated due to evaporation over a few years)
- They test CH ~monthly
- Draining the pool and refilling it is quite expensive in our area (my pool cost $3k to fill 5 years ago)
- Acid wash may remove 70-80% of the scale (visually) and would cost ~$2k
- The scale in the pool is only a cosmetic issue; no harm is being done
- They keep the pH low (7.2 - 7.4) to prevent scale buildup in the heater

And here’s what he said about the spa:
- Agreed that 0.5 ppm FC and 1.0 ppm CC; blamed it on the redwood tree debris that falls and sits in the pool for a few days between services (and from Sep - Nov I can confirm there is a lot of debris, seeds, …)
- Agreed that the service tech may not have added enough chlorine in the last visit, and informed me that I will have a new tech assigned, starting in 2 weeks

 

[Fedderman]

I suppose I could install a small water softener in-line with my pool’s auto-fill, to prevent more calcium from entering the pool. If this seems reasonable, then perhaps I’ll pursue the scale removal/water replacement process in the hopes of not having to do it again.

 

[ajw22]

Here’s what the pool service manager had to say about the scale:
- The majority of pools in my area have a high CH (concentrated due to evaporation over a few years)
- They test CH ~monthly
- Draining the pool and refilling it is quite expensive in our area (my pool cost $3k to fill 5 years ago)
- Acid wash may remove 70-80% of the scale (visually) and would cost ~$2k
- The scale in the pool is only a cosmetic issue; no harm is being done
- They keep the pH low (7.2 - 7.4) to prevent scale buildup in the heater

That all sounds reasonable. CH does not increase rapidly, and testing monthly is fine.

Acid washing reduces the life of your plaster.

You can spend money on draining your pool when CH gets high or replastering. Either is the cost of having a pool in your area.

And here’s what he said about the spa:
- Agreed that 0.5 ppm FC and 1.0 ppm CC; blamed it on the redwood tree debris that falls and sits in the pool for a few days between services (and from Sep - Nov I can confirm there is a lot of debris, seeds, …)
- Agreed that the service tech may not have added enough chlorine in the last visit, and informed me that I will have a new tech assigned, starting in 2 weeks

I think the cause is the tech not adding enough chlorine.

Debris is often blamed for low chlorine, but this is rarely the case. With an adequate chlorine level, tree debris is handled by normal sanitation.

I suppose I could install a small water softener in-line with my pool’s auto-fill, to prevent more calcium from entering the pool. If this seems reasonable, then perhaps I’ll pursue the scale removal/water replacement process in the hopes of not having to do it again.

Here is a recent discussion about using a portable RV water softener...

Portable water softeners

My CH seems to always be around 500-600. My fill water is around 250 (Austin Texas). My SWG cell seems to love calcium build up, requiring 2 or 3 cleanings per season, killing its life. Would something like this be effective on auto-fill line? This says "16,000 gallons" (which is about my...

www.troublefreepool.com

 

[Fedderman]

Here is a recent discussion about using a portable RV water softener...

Portable water softeners

My CH seems to always be around 500-600. My fill water is around 250 (Austin Texas). My SWG cell seems to love calcium build up, requiring 2 or 3 cleanings per season, killing its life. Would something like this be effective on auto-fill line? This says "16,000 gallons" (which is about my...

www.troublefreepool.com

Thanks, Allen - that is very helpful!

 

[Fedderman]

Here's what I'm considering: Perform an acid wash to remove the majority of the scale, then drain/replace the water to achieve the target CH and then install a water softener in-line with the pool autofill. I can sample the autofill CH ~monthly to know when to recharge it. I understand an acid wash reduces pool life, but if the water softener does its job, then I won't need to do it again.

 

[Fedderman]

Here's what I'm considering: Perform an acid wash to remove the majority of the scale, then drain/replace the water to achieve the target CH and then install a water softener in-line with the pool autofill. I can sample the autofill CH ~monthly to know when to recharge it. I understand an acid wash reduces pool life, but if the water softener does its job, then I won't need to do it again. I'm making a big assumption here, that the water softener will reduce my fill water CH from 50 to near-zero. I cannot seem to find any specs on the softener's output CH.

 

[Blackdirt Cowboy]

My well water calcium is 375 and my whole home water softener takes it down to 0.

 

[mknauss]

With a fill water CH of 50 and the amount of rain you get each year, I do not see why you need a water softener. I imagine your evaporation is not much more than one pool volume per year, and that would only raise your CH by 50 ppm. Then in the winter you can harvest some rain water and manage the CH rise pretty efficiently.

 

[Fedderman]

With a fill water CH of 50 and the amount of rain you get each year, I do not see why you need a water softener. I imagine your evaporation is not much more than one pool volume per year, and that would only raise your CH by 50 ppm. Then in the winter you can harvest some rain water and manage the CH rise pretty efficiently.

Thanks! The good news is that we had a lot of rain this past week (~8”) and the pool CH fell from 1125 to 850. That’s almost a 25% reduction, with more rain on the way. Seems much better than expected since the rainfall contributed well under 25% of the pool volume. I did my CH tests twice each time to make sure I was getting consistent results (since I’m a newbie at this), and I even used the standard sampler to make sure my measurement process was correct.

With a pool fill that is only 50 ppm CH, I’m struggling to understand how the CH got so high; the scale started being noticeable just 2 years after replastering.

 

[mknauss]

Either calcium was added via Cal Hypo, or the pH was run very low and calcium leached from the plaster, or your fill water chemistry changes during the different seasons.

 

[Fedderman]

Either calcium was added via Cal Hypo, or the pH was run very low and calcium leached from the plaster, or your fill water chemistry changes during the different seasons.

Thanks! I know they have been keeping the pH at the low end of the range. I’ll ask whether Cal Hypo was used, and I’ll periodically monitor the fill water CH.