Where to put acid/scale water?

[Enumjon]

Hi all. I have a spa that is connected via the plumbing system and a waterfall to our pool. The spa has scale buildup from the old owner - I have had the home for just over a year. Thanks to the plumbing hookup I can easily drain the spa into the pool and do an acid wash to remove the scale. My question is what to do with the acid/scale/water when the wash is done? Do I

1) Fill the spa back up and pump the water into the pool - the filter will take care of it.
2) Get a sump pump and send it out to the weeds.

Option 1 is much easier, but I am doubtful this is the best way to go. I assume I want to get that calcium out of the pool, not back in solution so it can form scale again.

 

[mknauss]

Any calcium you dissolve with the acid, if pumped into the bulk water, will raise the calcium level in that bulk water. So best to dispose of the water / spend acid. But be careful. Spent acid can still be quite harmful. And any acid wash will damage the plaster.

 

[Enumjon]

Thanks for the information, and warning. Is there another way to remove scale?

 

[Dirk]

And any acid wash will damage the plaster.

Please heed that carefully. Acid washing doesn't magically attack your scale and stains and ignore your finish. It eats away at both. Sometimes only removing stains because it removed a layer of your finish and took the stains with it. An acid wash completely destroyed my pool because the applicators didn't know what they were doing. They didn't test a small patch first, to see if the finish would hold up. They didn't adjust the pH of the solution (the strength of the acid wash) to minimize damage. They didn't quickly neutralize the puddle forming in the bottom as it collected, instead relying only on the dilution of the acid solution by hosing it off to do that, which it doesn't (water doesn't neutralize the acid and stop its reaction on your finish, it only dilutes it, which isn't the same thing).

I'll never acid wash again. If you're determined to do so, proceed with caution. Use only the minimum of acid to do the job, neutralize it (not just rinse it) very quickly. Don't let it sit on the bottom, etc. It's actually almost an art form, using just enough, applied just so, etc. Careful abrasion is sometimes the better solution (gently sanding off the scale down to where it's comfortable, not necessarily aesthetically perfect). That'll avoid the etching that even a well-done acid wash will leave behind, and be much more easily controlled.

And keep in mind, even the very best acid wash reduces the life of the finish by some amount. There is no way around that.

 

[Enumjon]

So can I go at it with an orbital sander? I understand that the acid dissolves everything, just like abrasion will remove everything. I tried some sanding by hand, but that was an exercise in futility. I am always a fan of power tools, but don't want to damage things. An orbital sander is the most gentle sander I have, will that do the job without damaging things?

 

[mknauss]

The best way to remove scale with the least chance of damage is a bead or soda blaster. Kieserite blasting is the best. It is costly.

 

[Enumjon]

FYI - this is just an aesthetic job. The scale has formed dark patches around the spa, so pretty thin layer. Don't really want to go for a costly blasting job, we rarely use the spa.

 

[mknauss]

Dark patches? Scale is white. Are you sure it is scale? Or is it scale embedded with iron and or copper?

 

[Enumjon]

Doh, you are right! I had white scale around the tile waterline which I removed easily with acid at the beginning of the year. I was just assuming all stains were scale, but this is a different color. I will have to figure out what the stains are before I tackle them.

 

[Dirk]

Sorry, I only know what to do next time, not how to do it. If I could go back, I would have left the scale alone. It didn't actually look any better after the wash, just different. Is the scale a visual issue, or a comfort issue? If the former, you might learn to appreciate it for its natural beauty! Otherwise, work on the areas that most affect comfort.

After my finish was replaced, (might have been during) the plaster guys blasted my edge tile. It was about $400, worth every penny.

 

[Enumjon]

I don't have a picture, but the stains are a sorta marbled color. Brownish with white and grey specks. Would be pretty cool looking for a countertop, or if the whole spa was that color. Not so good just in patches.

 

[Dirk]

Sorry, I'm one too many cooks here. You got the gist...

 

[duraleigh]

Before anything else, I think it makes sense to figure out how much acid you will use for the acid wash you are contemplating.

When you add acid to pool water your don't have spent acid and pool water.......you have pool water with a lower pH.......that's it

So, if you are using a gallon of acid to acid clean that spa and then drain it into your 30k pool, you are simply adding calcium (in solution) to your pool and a pH drop of somewhere around 1.0...........certainly not enough to do harm over the short term and easily brought back into the 7's (if necessary) with the use of 20 Mule team borax.

So I think an acid wash IS an option if you think through what you will be doing.

Last, I assume the spa is plaster and not fiberglass? It makes a big difference.

 

[mknauss]

Scale is raised and rough. Stains are not.

 

[Enumjon]

Spa is plaster, as is the pool. I am pretty comfortable with acid - muriatic acid that is. Have put over 30 gallons in the pool so far this year, and my TA is still around 200. Calcium level is in the upper end of acceptable, so I would rather not add more calcium to the pool. But it seems this is a mineral stain, not calcium scale, so I need to do a little investigation.

This actually makes good sense. In the spring when I was done washing the tile line I did a half-hearted job on the spa. The MA didn't do anything to the stains. At the time I just though I had to come back and hit it harder, but it sounds like I need a smarter approach. Or I may just take Dirk's sage advice, and leave it be.

 

[mknauss]

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