Scale weirdness

[Looki]

Hey all

I am currently at my wits end with my pool and pool contractor. Every spring when I bring the pool out hibernation I find the pool walls and floor are covered in scale. Not sure what is causing this to happen.

Pool is a 20000 gallon concrete shell pool with a marsite plaster finish.
It is a salt water pool.
It has a auto cover over the pool through out the winter that is not opened for roughly 6 months.
Pool is winterized by my pool contractor each fall.
The water is not circulated in the winter season what so ever.

The scale is strange in that it mostly forms on the bottom at the deep end of the pool and up the walls roughly 4 ft. There is scale above this line but it is less dramatic.
The scale is so sever that I have to drain the pool and sand it down as it will cut swimmers.
The pool is 4 years old and it has done this each and every year.
The scale does not reoccur through the swimming season.
The water is city water and is considered soft water with out much in the way of metals.

Any one else ever run into scale forming in cold water?

The pool shell hangs over the edge of a rock cliff and is exposed to air all the way around in the winter.


Thanks in advance.

Looki

 

[zea3]

What were the CH, pH, and TA when you opened the pool?

 

[duraleigh]

Not sure what is causing this to happen.

High pH, higfh CH and high TA are the cause. The opposite of that is the cure

 

[pooldv]

More here on scale and managing it.
Pool School - Calcium Scaling

 

[Mark DeShaw]

I am the pool operator for this client and wish to add some flesh to the bones of our problem:

The pool chemistry has been kept following Langelier Index parameters, keeping calcium under 350 ppm and alkalinity between 80 and 120 at all times. The pool is kept quite warm (86-90) in the summer but as has been mentioned, the "scaling" seems to manifest over the winter when the water is ~50 deg.
Other notables:
- salt content never exceeds 3500
- a year after first bout of scale, we learned about phosphate scaling and - sure enough - phosphates were through the roof. Natural Chemistry product was used to eliminate all phosphates and they have not been present in the pool since.
- pool water has always had a continually rising pH, due in part to salt chlorination but also (I suspect) due to plaster shedding calcium carbonate

Why it's so weird:
1. Scale manifests in winter when water is cold
2. Is concentrated starting at about 3' of depth and deeper. In fact, you can visually see the transition point!
3. Happened again last season and over winter while deliberately keeping pH between 7.1 and 7.4; calcium below 150 ppm

After eliminating the phosphates, the only other culprits we can think of are the plaster mix and the waterproofing membrane applied (Aquafin trowel on/roll-on cementitious acrylic)...

Thoroughly stumped in Victoria!

 

[Looki]

Bump...

I am the pool operator for this client and wish to add some flesh to the bones of our problem:

The pool chemistry has been kept following Langelier Index parameters, keeping calcium under 350 ppm and alkalinity between 80 and 120 at all times. The pool is kept quite warm (86-90) in the summer but as has been mentioned, the "scaling" seems to manifest over the winter when the water is ~50 deg.
Other notables:
- salt content never exceeds 3500
- a year after first bout of scale, we learned about phosphate scaling and - sure enough - phosphates were through the roof. Natural Chemistry product was used to eliminate all phosphates and they have not been present in the pool since.
- pool water has always had a continually rising pH, due in part to salt chlorination but also (I suspect) due to plaster shedding calcium carbonate

Why it's so weird:
1. Scale manifests in winter when water is cold
2. Is concentrated starting at about 3' of depth and deeper. In fact, you can visually see the transition point!
3. Happened again last season and over winter while deliberately keeping pH between 7.1 and 7.4; calcium below 150 ppm

After eliminating the phosphates, the only other culprits we can think of are the plaster mix and the waterproofing membrane applied (Aquafin trowel on/roll-on cementitious acrylic)...

Thoroughly stumped in Victoria!

 

[duraleigh]

Who is testing the pH in the winter?