Mineral Scale on Above Ground Pool Liner ... Calcium Hypochlorite?

[Mr. Fixer]

Hello all,

When I opened last year I shocked my pool with Calcium Hypochlorite. A lot over about a week trying to knock down an algae bloom. I then added acid to adjust the ph. It dropped a bit to low. When I added Borax to bring it back up it instantly produced a milky colored cloud that spread quickly throughout the pool. I'm guessing it's calcium from the shock. It cleared up in a few days but left a scale on the sides of the liner. We were able to brush it off the top 2/3s of the liner fairly easily but the bottom 1/3 is much denser. The pool brush was ineffective on the bottom 1/3. The scale can scratched off with your nail. I'm hoping I can lower my PH while opening the pool this year to try and bring the scale back into solution. Any thoughts or advice would be appreciated.

THX

 

[duraleigh]

This advice is meaningless unless you post valid test results from a reliable kit we can trust. That said.....

That is certainly what I would try. You seem to have a grasp of the chemistry so assuming you are CAREFUL with your doses, I would walk the pool down to 6.8 pH and then hold it there very accurately for a week or so (probably not longer) to see what progress you can make.....brushing every couple of days.

 

[Mr. Fixer]

Thanks, Dave

How concerned should I be about my vinyl liner at a 6.8 PH? I'm guessing the short term shouldn't be a problem.

 

[duraleigh]

Test results, please.....especially CH

 

[Mr. Fixer]

Here's what I've got Dave;

CH 125
TA 110
PH 7.0
Chorine 5+
FC 4
CYA unknown (waiting on delivery of reagent)

 

[duraleigh]

Interesting numbers. Are you chlorinating with pucks?......I am just mildly curious about your lower than average pH.

So, your CH is quite low and putting more CH into solution will have little negative affect......you have plenty of wiggle room.

Will a pH of 7.0 for 3-4 weeks hurt your liner? No

How about 6.8? probably not but it is too low for that long so I wouldn't do that.

How about 6.6? Perhaps not but you are getting too low for sure with that time period of 3-4 weeks.....Don't do that!

How about 6.4 for 24 hours? Should be no problem.

So, you see it is a matter of the actual pH AND how long you leave the pH at that level. 6.8 for one week will not cause any harm and I believe, with some brushing, will get rid of the scale.

 

[Mr. Fixer]

No, I've never used pucks. I made the mistake of listening to the guy at the pool store and used calcium hypochlorite last year when I opened and slammed the pool.

Yesterday, I pulled the cover off. topped it off with the hose (Chicago municipal) started the filter and added 8 gallons of 12.5% sodium hypochlorite. Not sure why the ph is low. I'll walk the ph down to 6.8 and start brushing. Thanks for the help. I'll keep you posted on the results.

 

[duraleigh]

I would test pH probably twice daily during this week just to make sure you don't let it slip lower than you intend. It sounds like you have a good grasp on your testing and dosing so I think it will go well.

 

[Mr. Fixer]

Will do. Thanks Dave!

 

[Mr. Fixer]

Hello Dave,

I just wanted to update you on the results. I walked the PH down to 6.8 and held it there for a few days and tried brushing. With considerable effort, we made little progress. I decided to abandon the operation as it seems mostly cosmetic and the masses were getting restless about getting to use the pool. Thanks again for your input.

 

[duraleigh]

You're welcome. Since 7.0 is safe all the way around, I think I would try to hold it there for maybe the whole swim season and spend little if any physical effort. I believe 7.0 will dissolve the scale.....although VERY slowly.

 

[cj133]

For what it's worth, for 20 years the only "chlorine" my dad ever used was Cal Hypo. He would buy it in I think a 65 pound or 75 pound bucket.

There were never any issues with scale in his case.

But water varies greatly. I've been tempted to buy some Cal Hypo for SLAMing etc but my water is on the harder side so I keep avoiding it.
Point being, I don't know that the advise you received was necessarily bad.