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Funky Problems in the Field

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Funky Problems in the Field

Yeah, you know what you are doing, but, in the field, you get some zingers.  This group is set up as a forum to discuss those weird and wacky problems that everyone runs into and the solutions that saved the day!

Members: 21
Latest Activity: Aug 20, 2016

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SALT CELL FAILURE 2 Replies

I have a problem to solve.1. 15000 gallon negative edge pool2. pump and filter systems (1. variable speed intelliflow and one 4x160 on large sand filters )3. Below water level of pool 4.6 ft4. 2…Continue

Started by Michael Flanagan. Last reply by Rex Richard Jun 20, 2012.

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Comment by Richard A. Falk on August 20, 2016 at 2:35am

An attached spa with spillover will creation aeration of the water that will tend to have the pH rise especially if the TA isn't kept low.  If you are only testing and adjusting the chemistry once a week, the pH may be higher before you adjust it.  During that higher pH and therefore higher CSI time then if the heater was run it might have built up scale.  Not a lot, but a little each time this occurred.  If you didn't have the CSI be negative at other times then such scale would stay on the heater and not dissolve into the water.

As to why it started to dislodge now, that's more of a mystery.  Perhaps enough built up that some mechanical stresses from pump on/off water flow dislodged it.  Or maybe there have been periods of lower CSI now compared to before or some other chemical that dislodges scale was added (including various surfactant chemicals).

Comment by Charles Allen on August 19, 2016 at 5:21am

well that is thorough

without a doubt the CH of this pool has never been higher than 250 since its construction

phosphates are not existent now and for the past yaear or so

and have never gone over maybe 1,000ppb

So i am going to try the low LSI level for a couple of weeks

see if this rids the pool of that problem

BUT - i still dont think i have a bead on the cause here ? so as a parting comment on this situation - can you try and explain how this happened?

the chemicals have always been withing proper parameters

the heater has been run, of course, but not all that frequently

all of the things you have alluded to as to possible chemical parameters being off that could have lead to this are out of play - CH, TA, pH, CYA, Salt Levels - all of those have been within paramters / heater not run all that  much / new cell / newish heater

what do you think the cause could be here?  if you had to guess, knowing that chemicals have been within proper parameters all the time - what would your best guess be as to the cause

Comment by Richard A. Falk on August 18, 2016 at 3:56pm

It takes rather high calcium and phosphate levels to get calcium phosphate scale.  The acid test is pretty definitive since calcium carbonate will fizz (producing carbon dioxide gas) while calcium phosphate will not.

It's a good suggestion to check in general, though.  The following link has a graph and formula for the saturation level of calcium phosphate:

http://msdssearch.dow.com/PublishedLiteratureDOWCOM/dh_0060/0901b80...

which shows that even at a pH of 8 and 30C (86F) and a CH of 1000 ppm that it would take 4 ppm (4000 ppb) phosphate to start getting calcium phosphate scale so while possible when using HEDP-based metal sequestrants it isn't nearly as common as calcium carbonate scale.  At 17C (30F) hotter, with the pH of 8 and CH of 1000 scale could form at 1.65 ppm (1650 ppb).

Calcium phosphate scale is usually harder to remove than calcium carbonate.

Comment by Terry Arko on August 18, 2016 at 9:25am

Sounds like you are on the right track and Richard is definitely the one to help with this. You may want to take some of the white powdery stuff to a lab and see if it is calcium phosphate, do a test of your water for phosphate levels as well. We have seen some cases where in high ortho-phosphates combined with calcium and calcium phosphate forms on heat exchanger. This primarily was observed when high phosphonic or phosphoric acid scale and metal products were frequently used or buffered acids that contain sodium phosphate as a buffer. It may help to check your phosphate level and if high have it lowered and use a scale inhibitor that is non-phosphate based such as EDTA.

Comment by Charles Allen on August 18, 2016 at 8:30am

thank you for all of your help Richard!  i really appreciate it

will give the low LSI for a week or so and will report back to you!


Comment by Richard A. Falk on August 17, 2016 at 3:07pm

Yes, a CSI of around -0.6 should dissolve the calcium carbonate scale.  If you have to you can use a scale inhibitor product designed to remove scale as that will make the process go faster, but a low CSI should do the trick.  If you only do this for a few weeks until you don't see any more scale, that shouldn't be too long with regards to plaster.  It takes months to years of low CSI to degrade plaster unless the pH is very low (i.e. Trichlor pools where the TA is exhausted and the pH crashes).  At least for plaster that is cured -- you don't want the CSI low for new plaster as new plaster is still pretty soft and will dissolve more readily even at -0.6 CSI.

Comment by Charles Allen on August 17, 2016 at 1:56pm

dropping ph to 7.0 and TA to 80 would make LSI read about -.65

to swimmer, that would be tolerable at 7.0 - would the -.65 be sufficient to "burn off" the Calcium Carbonate?

Comment by Charles Allen on August 17, 2016 at 1:49pm

very strange though

LSI is .14 and has been checked and monitored weekly

heater works but has not been run in months

all chems test within parameters and salt levels are at recommended levels

filters recently cleaned

brand new salt cell

but the powder i pulled out fizzed and turned yellow when i put Muriatic Acid in test container with powder

this is a fairly recent phenomenon in this pool - operated for 4 years without any of this kind of a problem yet about 2 months ago this started happening

all along the LSI has been at about that .14 mark and all along chems were maintained

heater may have been turned on about 3 months ago and left runing for a couple of weeks - to "prime the pool" for swimming - but since then - the heater has not run

do i just "take the powder out" and flush the heater?

will it eventually dissipate?

should i run the pH at about 7.0 for a few days (or is that acidic enough?  maybe lower?  what level?

any other advice would be much appreciated - and am i the only guy to have experienced this out there?

Comment by Richard A. Falk on August 17, 2016 at 9:06am

The temperature at the surface of a heat exchanger will be around 30 degrees Fahrenheit higher than the bulk pool water so the saturation index will be around +0.2 units higher than the bulk pool water.  That by itself with balanced pool water would probably not scale so I suspect that at some point either the bulk pool water had a higher saturation index especially when the heater was being used or perhaps someone added some chemicals to the skimmer such as pH Up (sodium carbonate) or Calcium Hardness increaser (calcium chloride), but not just one time but regularly.  This could have happened quite a while ago and the only reason you're seeing the sloughing off now is that your saturation index is lower than before (or someone added acid through the skimmer).

Comment by Charles Allen on August 17, 2016 at 8:17am

EUREKA - Definitely Calcium Carbonate

now what?  how did the calcite saturation index get above that 0 amount?  in your experience?

and thanks for you help - btw

 

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