Plaster Pool Roughness

[Rasalon]

Greetings!

I have a SWG 25K gallon pool, built in 2003, that was acid washed in May of 2009. For the whole of 2009, the pool was great, just required the continual addition of acid as the pH had a tendency to climb.

When I closed the pool, all chemical levels were within range. Plus I have an automatic pool cover, so the pool gets sealed pretty tight with very little water/contaminants entering.

When I opened the pool earlier in May, the water was pretty clear, but the sides of the pool were covered in little white crystals. They brushed off easily. However, my steps are now very rough, about the consistency of 80 grit sand paper. They were so smooth when I closed. Plus the pool cleaner is picking up a lot of these white crystals. They look like pure white sand, don't taste very salty, and crush into powder pretty easily.

When I opened the pool, initial tests showed high pH (8.8) and high TA (180). I only had to run my SWG on super chlorinate for 2 days to get FC to start registering.

So what did I do wrong and what do I need to do to correct it? Below are my current pool chemical readings. I have the TF-100 kit, along with a LaMotte digital reader (which I trust with having the highest accuracy):

- Water is currently 80 degrees
- Salt is at 3800 ppm
- pH is at 7.0 (LaMotte states 7.1)
- TA is between 70 and 80 (solution turns pink at 7 drops, darker pink at 8 drops, no change in color with additional drops)
- FC is at 1.0
- FC using DPD states chlorine at 2.0
- CC using DPD at 0.5
- CH is at 370
- CYA is <20
- Phosphates are at 200 ppb
- Copper is about 0.3 ppm
- Iron is at 0

Other than stabilizer, is there anything else I need to adjust? Anything I can do to correct my rough steps? And what do I need to do at closing to prevent this from happening again? Thanks for any advice, I am baffled as I take very good care of my pool, whereas neighbors only test their pool using pool test strips once a month, and don't have these issues. Thank you!

- Jason

 

[dykes26]

Not at all an expert but If the PH was low as you say for a long period of time you might have gotten plaster corrosion or pitting of the plaster.

 

[duraleigh]

When I opened the pool, initial tests showed high pH (8.8) and high TA (180).

You cannot let your pH get that high. You have calcium precipitation (scaling). Your CH of 370 is not over the top but on the higher side of normal and it will turn into a solid and stick to the floors and walls (steps) when the pH is that high. pH should never be allow to exceed 7.8 for any length of time.

I assume that's why the pool was acid washed in 2009 as well.

From anecdotal evidence, the LaMotte colorQ doesn't seem to be as accurate as the drops-based kits with the CH test and the CYA test. I'm not sure how it compares during the pH, TA, and FC tests.

 

[Rasalon]

When I opened the pool, initial tests showed high pH (8.8) and high TA (180).

You cannot let your pH get that high. You have calcium precipitation (scaling). Your CH of 370 is not over the top but on the higher side of normal and it will turn into a solid and stick to the floors and walls (steps) when the pH is that high. pH should never be allow to exceed 7.8 for any length of time.

When I closed the pool, the pH was at 7.2 and the TA at 110. Does this mean I should check and adjust pH mid-winter going forward?

From anecdotal evidence, the LaMotte colorQ doesn't seem to be as accurate as the drops-based kits with the CH test and the CYA test. I'm not sure how it compares during the pH, TA, and FC tests.

Actually, I have the LaMotte 1749 TDS/pH tester, it doesn't give any other readings. But I keep it very well calibrated, which is why I trust its pH readings the most.

Thanks!

 

[frustratedpoolmom]

Do you have a way you can check and circulate the water mid winter? I would think it unlikely the problem would happen again next winter - as enough time should have passed after the acid wash. But if you can circulate, test and adjust if necessary then it can't hurt.

I concur with Dave sounds like scale - the crystals/sandpaper feel won't brush off the steps area?

 

[Rasalon]

Do you have a way you can check and circulate the water mid winter?

It would be difficult, as I live in the the northeast (NJ), so the pool water is drained below the skimmers, all the lines are blown out and plugged, and the filter and chlorinator come apart and are stored inside for the winter.

I concur with Dave sounds like scale - the crystals/sandpaper feel won't brush off the steps area?

All the crystals brushed off pretty easily, but I tried a wire pool brush on the step, and it had no effect on the roughness.

Since the roughness is only isolated to the steps, does anyone know if liquid scale remover poured onto the steps would help? Thanks again for everyone's advice.

 

[frustratedpoolmom]

That I don't know - I'm not familiar with the product. Maybe someone else who has tried it will advise.

Some people use submersible pumps to circulate the water, test, and adjust if necessary. You can pick up ones for around $100. Something to consider if you feel it's worthwhile.

 

[duraleigh]

When I closed the pool, the pH was at 7.2 and the TA at 110. Does this mean I should check and adjust pH mid-winter going forward?

Yeah, you will have to do something or I suppose the same thing will happen next winter. I have no idea what would cause that huge jump but it's an issue you will need to deal with. Was the acid wash for the same reason? Scale?

I have never tried the liquid but I would assume it is simply a very low pH and will likely dilute into the pool. I have no idea it will be successful.

What you might try is lowering your pH CAREFULLY down around 6.8 or even 6.6 since you have the ability to monitor and adjust very precisely. Held down that low over a period of a week or two might remove the scale from the steps if the liquid doesn't work. I don't think I would go quite that low if you have a heater in the sytem

 

[Rasalon]

Some people use submersible pumps to circulate the water, test, and adjust if necessary. You can pick up ones for around $100. Something to consider if you feel it's worthwhile.

Heh, I already have a 1800 gph back-up submersible pump, never thought of using it as a pool circulation pump, but with a garden house, it should work fine. Thanks!

 

[Rasalon]

Was the acid wash for the same reason? Scale?

It was the first time the pool was ever acid washed, and it was to remove the scale build-up along the winter water line, below the tiles. After the acid wash, the plaster looked great, plus it allowed for a detailed inspection showing no plaster cracks/bubbles/peels.

What you might try is lowering your pH CAREFULLY down around 6.8 or even 6.6 since you have the ability to monitor and adjust very precisely. Held down that low over a period of a week or two might remove the scale from the steps if the liquid doesn't work. I don't think I would go quite that low if you have a heater in the sytem

I have solar heating, but that is all PVC, so wouldn't be affected. My pH is already low (7.0 - 7.1), so it isn't that far from 6.6, maybe now is the time to do it. By carefully lowering pH, I assume you mean repeatedly adding acid over the two week period to keep the pH low but try to not bring down the TA? If I dropped in a gallon of acid today, it would easily get the pH low enough, but would drag down the TA a good 20 to 40 points, which I want to avoid

Thanks!

 

[duraleigh]

I assume you mean repeatedly adding acid over the two week period to keep the pH low but try to not bring down the TA? If I dropped in a gallon of acid today, it would easily get the pH low enough, but would drag down the TA a good 20 to 40 points, which I want to avoid

Yikes!! Don't add a gallon. I calculate about 1.5 quarts would bring pH down to around 6.8 from your current 7.1.

If you choose to lower into the high 6's(pH) for scale control, it should be done very carefully and monitered carefully as well. You can easily re-elevate your TA with Baking Soda and it will have little affect on your pH.

 

[Rasalon]

I have been doing as suggested, keeping my pH low, to get rid of the calcium scaling that has already occurred.

My pool readings are pretty much the same as in my first post (TA around 80, pH around 6.8), and the scale is being removed SLOWLY. However, my DE filter keeps clogging up with little white "stuff", that backwashing does not remove, I am assuming it is calcium particulates (it is like a very fine bright white sand). Therefore, I have to keep disassembling my filter and rinsing the elements, sometimes with muriatic acid to get them clean.

My normal filter pressure is around 3psi (I have the Pentair Intelliflo and solar panels, so my my flow is lazy 30gpm), but within a few days it can get up to 25psi.

What doesn't make sense is I have probably replaced about 25% of the water in the pool through frequent backwashes, but there are no decreases in the clogging intervals. I am spending a small fortune on DE. Last year, my pool pressure was a steady 3 to 4psi all summer, with one or two backwashes.

At this point, am I just better off just emptying the pool, acid washing the remaining scale off, and refilling from water supply, then rebalancing? This is my fourth year of this pool, and it has never been this bad, and I haven't been doing anything different this year than previous years. Thanks!