Calcium scaling and high LSI. How should I fix this?

[Ack]

My pool has developed a rough, sandpaper-like texture on the plaster surfaces that used to be smooth. Correct me if I'm wrong, but I assume this is scaling. I also have white staining on the tile at the waterline.

It's a non-saltwater plaster pool using Chlorine. The pool is a couple of years old and the pH tends to creep upward if I don't stay on top of it. I assume that it got high and stayed high over the winter while the pool was closed.

My CH seems rather high, probably because I've been using cal-hypo.

My current levels are:

Temp: high 80's to low 90's. Currently 92.
FC: 7-10 (try to keep it around 10.)
pH: 7.6 (I try to keep it right at 7.6 with daily testing, and have been for the past 2 months since we opened)
TA: 90
CH: 350
CYA: 70

If my calculations are correct, this gives me an LSI of 0.41, which can cause scale.

So, two questions:

1. What's the best way of going about changing the levels above to get the LSI to a balanced level that won't cause scale?

2. What's the best way to remove the scale that has already formed on the plaster?

 

[Bama Rambler]

The easiest and best thing to do is lower the pH to about 7.2 and do your best to keep it under 7.5 all the time.

 

[linen]

Bama beat me, but here is my take...use poolcalculator.com to calculate your CSI (calcite saturation index). According to the poolcalculator.com your csi is ~0.09 which is right in the middle (and should not cause scale), but that doesn't mean your CSI has always been good. See this pool school article: http://www.troublefreepool.com/pool-school/calcium_scaling

By the way, your CH level is not too bad...but I would stop using the cal-hypo and switch to bleach/liquid chlorine to chlorinate.

 

[jblizzle]

Not related to your question, which Dave covered, but:
Is there a reason you are keeping your FC so high? Minimum is 5ppm for your CYA of 70ppm. For that matter, is there a reason you have your CYA so high for a non-SWG pool?

 

[Ack]

The easiest and best thing to do is lower the pH to about 7.2 and do your best to keep it under 7.5 all the time.

Will this eventually remove the existing scale, or just prevent more from forming? Is it safe to swim in with a pH of 7.2?

Is there a reason you are keeping your FC so high? Minimum is 5ppm for your CYA of 70ppm. For that matter, is there a reason you have your CYA so high for a non-SWG pool?

For some reason I had it in my head that the CYA chart said 10 FC at 70 CYA. Looking again I see that it should actually be at 8 FC. I'll correct this. Thanks!

I have the CYA so high because the pool is in full sun all day and we live in a very hot, sunny area. The FC level drops extremely fast. I assumed that a higher CYA level was the best way to slow down the breakdown of the Chlorine. Please tell me if I'm wrong and should lower the CYA!

According to the poolcalculator.com your csi is ~0.09 which is right in the middle (and should not cause scale), but that doesn't mean your CSI has always been good. See this pool school article: http://www.troublefreepool.com/pool-school/metal stains

My CSI is "balanced" but my LSI is "scale". Which one should I believe?

I looked at the Metal Stains article you linked but it seems to be discussing Iron and Copper stains, not scaling. Am I missing something?

Thanks, everyone!

 

[Bama Rambler]

If you keep the pH at 7.2 it will eventually remove the scale that has formed. It is a slow process but it will happen.

It's perfectly safe to swim at 7.2 pH.

 

[jblizzle]

Yes, pH of 7.2 is perfectly safe and if you maintain a negative CSI (we do not look at LSI) and brush a lot, the scale should diminish ... but we are talking about years timeframe, not days here. If you want is removed immediately, you would have to do an acid wash.

You are right that the higher CYA should protect the FC better from the sun. The only issue with higher CYA levels is that the shock level required for the SLAM process gets to be pretty high if you develop a problem.

I think linen meant this article (just above the metal one in Pool School): pool-school/calcium_scaling

 

[linen]

I think linen meant this article (just above the metal one in Pool School): pool-school/calcium_scaling

Yep I did ...fixed now.

 

[Ack]

Thanks, everyone. I'll maintain pH at 7.2, brush often, and hope for the best.

What's the lowest pH at which it's safe to swim? (In case I mess up occasionally).

 

[jblizzle]

Keep the pH above 7 so it is measurable ... although should be "safe" even below that some.

 

[chem geek]

My CSI is "balanced" but my LSI is "scale". Which one should I believe?

You need to adjust the TA for the CYA level. The CSI and LSI calculations uses the adjusted TA. The Pool Calculator does this automatically for you. If you are using the Taylor watergram or something similar, they expect you to adjust the TA based on your CYA level. At your CYA and pH, you would lower the TA by 24 ppm -- the rough rule-of-thumb is to subtract 1/3rd of the CYA level from the TA to get carbonate alkalinity used in the LSI calculation.

Even if your CSI or LSI were a little high, you usually don't get scale from that so something doesn't sound right about this situation.

 

[Ack]

Even if your CSI or LSI were a little high, you usually don't get scale from that so something doesn't sound right about this situation.

The pH in my pool tends to naturally creep up pretty quickly. I suspect that the pH level got pretty high over the winter while the pool was closed and then sat that way for months. I can't be sure though because the pool company that opens the pool for me dumped in some acid before I could measure anything.

 

[chem geek]

Oh, in that case, then it's possible, if the pH went quite high.