Does dissolving calcium scale on the tile with diluted acid damage the tile itself & does it contribute to lowering alkalinity (or adding calcium)?

[Gary Davis]

I'm just curious about three related questions given I need to add massive amounts of acid to my fill water to lower the high alkalinity to a more manageable range.

1. Does dissolving calcium scale on the tile with diluted acid damage the tile or grout itself?
2. Does using the calculated amount of acid to lower alkalinity contribute to alkalinity by dissolving the scale into the water?
3. Does the HCl chemically remain active to "burn" off alkalinity if it's first used to dissolve the tile calcium scale?

These are esoteric questions, which, if I knew chemistry better, I could probably answer them myself.
Anyone have any idea if using the acid on the tile helps or hurts (or doesn't matter) to the goal of lowing alkalinity with acid in the first place?

 

[Rocket J Squirrel]

1. I have poured straight MA on a scrubber to remove scale and never seen any damage caused. It gets diluted pretty quickly.
2. Simply adding more MA to the the water is unlikely to dissolve scale. It needs scrubbing.
2a. A little MA on a scrubber will not increase your measurable MA.
3. I don't understand the question. One of our experts probably will.

 

[JamesW]

Does dissolving calcium scale on the tile with diluted acid damage the tile or grout itself?

It can depending on the tile and grout.

Does using the calculated amount of acid to lower alkalinity contribute to alkalinity by dissolving the scale into the water?

1 lb of calcium carbonate adds 4.78 ppm of calcium and 4.78 ppm of total alkalinity to 25,000 gallons of water.

1 gram of calcium carbonate adds 0.011 ppm of calcium and 0.011 ppm of total alkalinity to 25,000 gallons of water.

Hydrochloric acid dissolves calcium carbonate and only the calcium and chloride will remain assuming a 2:1 molar ratio.

2HCL + CaCO₃ --> Ca²⁺ + H₂O + CO₂ + 2Cl^-

You might get some very minor amounts of bicarbonate.

HCL + CaCO₃ --> Ca²⁺ + HCO₃^- + Cl^-

Overall, you won't end up with any added alkalinity.

The effect will be neutral or a lowering of TA.

Does the HCl chemically remain active to "burn" off alkalinity if it's first used to dissolve the tile calcium scale?

If you use excess acid above the stochiometric ratio, the excess acid will lower the TA.

The CH (Calcium Hardness) and salinity will increase.

 

[Gary Davis]

1. I have poured straight MA on a scrubber to remove scale and never seen any damage caused. It gets diluted pretty quickly.

Thanks. I purposefully kept the water level at the tile-to-pool line so that I could spritz every tile with diluted acid, which cleaned most of the tiles.
What's left is a VERY WHITE (super white, super thin, almost dusty) substance which doesn't dissolve in acid - so it must not be calcium carbonate.

2. Simply adding more MA to the the water is unlikely to dissolve scale. It needs scrubbing.

I spritzed all of the tiles without scrubbing, which took hours but they eventually dissolved all the "scale" on the lower half of each tile (I don't know what the very white powder is on the top half of the tile though), but the scale was so thick on the skimmer that I had to pour undiluted HASA muriatic acid on the flats which bubbled away the scale without any scrubbing needed.

2a. A little MA on a scrubber will not increase your measurable MA.
3. I don't understand the question. One of our experts probably will.

I see that JamesW understood the chemistry questions, so I will look at them closely to learn from his wisdom.

 

[Gary Davis]

It can depending on the tile and grout.

Thanks for explaining that the tile & grout can be damaged. The tile seems impervious to the acid, while the grout definitely bubbles.
After a few days of spritzing diluted acid, nothing bubbles anymore - but something powdery white is left on the upper portions of the tiles.

1 lb of calcium carbonate adds 4.78 ppm of calcium and 4.78 ppm of total alkalinity to 25,000 gallons of water.

Oh. That's interesting. Very interesting. Thanks for running the math - which I don't have the chemistry or physics knowledge to ascertain on my own.
Much appreciated the kind help!

I hadn't thought of that. I'm used to adding Calcium Chloride (where my calcium is currently at 250ppm), which apparently doesn't increase the alkalinity (which, at the moment, is about 150ppm) - but - this tile scale is likely Calcium Carbonate, which does both increase calcium & alkalinity (where my overarching goal for the water balance is less alkalinity but more calcium in a ratio somewhere around 4:1 if possible).

I'm going to guess I've added nowhere near a pound of calcium carbonate, as the scale must add up but it is a very thin layer less than a tenth of a millimeter or so on each time and even then, only on the bottom half of each tile (the top half has a white powdery non-acid-reacting substance on it).

1 gram of calcium carbonate adds 0.011 ppm of calcium and 0.011 ppm of total alkalinity to 25,000 gallons of water.

Ah, very good. It's easy for me to decide when you give me the numbers like that. It's really not adding much at all, as I'm going to guess I've added less than about 50 grams of calcium carbonate to the pool by dissolving all the scale on the tiles, so the addition of calcium will be negligible, but at least in the right direction.

I am trying to get rid of alkalinity, so the end result appears to be a wash in terms of adding calcium (which I want to raise) but also adding alkalinity (which I want to lower).

Hydrochloric acid dissolves calcium carbonate and only the calcium and chloride will remain assuming a 2:1 molar ratio.

2HCL + CaCO₃ --> Ca²⁺ + H₂O + CO₂ + 2Cl^-

You might get some very minor amounts of bicarbonate.

HCL + CaCO₃ --> Ca²⁺ + HCO₃^- + Cl^-

Overall, you won't end up with any added alkalinity.

This is the summary that matters a lot since I'm adding acid to dissolve the scale where the acid dissolves the scale (which increases the alkalinity) but the acid also burns off the calcium carbonate in the water (which decreases alkalinity). Overall I've added three gallons of acid (mostly diluted and spritzed on the tiles) over the past week, so my alkalinity has lowered from 270 originally in the fill water to about 150 currently (and I have more acid to add but I no longer need to clean the tiles of the scale).

The effect will be neutral or a lowering of TA.
If you use excess acid above the stochiometric ratio, the excess acid will lower the TA.
The CH (Calcium Hardness) and salinity will increase.

Thank you very much for your astute educated assessment of the effect of adding a few gallons of HASA muriatic acid to clean the scale off of the tiles.
Overall, the alkalinity and calcium hardness are moving (slowly) in the direction I need them to go (i.e., alkalinity down & calcium up), where I'm aiming for a 1:4 ratio but I doubt I'll ever get there due to the excessive amounts of acid needed - where mostly I wanted to clean the tile while I was adding the muriatic acid anyway.

Thank you very much for your helpful and kind advice!