Calcium on a negative edge wall, and on tile that is only a year old

A negative edge (also called a vanishing or infinity edge) is the one place on a pool where calcium does not stay politely at the waterline. If the tile on your edge wall is crusted top to bottom while the waterline band on the other three sides is merely dull, that is normal for this design in Chandler water, and it needs a slightly different job than ordinary pool tile cleaning.

Why the edge wall scales across its whole face

On the rest of the pool, scale forms in one band where water meets air. On a negative edge, water spills over the weir and runs down the wall face into the catch basin every hour the pump runs. Two things happen in that thin sheet:

It evaporates fast. A film spread over a wall loses water to dry Valley air far faster than the still surface of the pool, and evaporation leaves every bit of dissolved calcium behind on the tile.

It gives up carbon dioxide. Water tumbling over an edge outgasses CO2, which raises its pH right at the tile. Higher pH is exactly the condition that pushes calcium carbonate out of solution. Waterfalls, scuppers, and spillways crust for the same reason.

The result is scale over the entire wet face of the wall, plus a ring in the catch basin wherever its level rises and falls between pump cycles.

Why tile that is only a year old can already be crusted

We hear this one after remodels. Three things stack up in the first year:

• The refill. A replaster or retile almost always ends with a full refill from the hose, so the pool starts at full tap-water hardness instead of the partly balanced water it had before.
• The cure. Fresh plaster releases calcium into the water while it cures, which pushes hardness and pH up during the same months the new tile is going in.
• The summer. A Chandler summer then evaporates a lot of that water away and the top-ups add more hard water, as described on the waterline calcium page.

None of that is a fault in the tile or the tile setter. It does mean that cleaning alone buys you a season, not a cure, unless calcium hardness and alkalinity are brought back into range afterwards.

How we take it off

First, the fizz test. A drop of muriatic acid on the deposit tells carbonate (fizzes) from silicate (does not), and that decides the method. Carbonate on young tile usually fizzes.

The waterline band is done the usual way: water lowered a few inches, then bead blasting or a targeted acid treatment.

The edge wall and catch basin are worked with the pump off so the wall stops running, from the catch basin side. Depending on how your basin is built that can mean lowering the basin, not the pool.

Glass tile is softer than porcelain and frosts under the wrong media or pressure, so the media is chosen for it. Tell us it is glass when you send photos.

Grout lines on the edge wall hold scale too; a clean tile face with white grout lines left in it reads as unfinished, so they are part of the job.

What to send for a quote

• The length of the waterline tile band in feet.
• The length of the edge wall and roughly how tall the tiled face is, since the wall is often longer than the waterline and the height decides the area.
• A close photo of each, and one from the deck showing the catch basin.
• Whether the edge tile is glass or porcelain, and whether the deposit fizzed.

Pricing starts from the published tile cleaning range of $200 to $500, with heavy scale often priced per linear foot, and a negative edge sits at the large end or above that because it is a second run of tile plus the basin. See the pricing page for the full table and calcium and scale removal if the plaster has scaled too.

Keeping it off

• Test after any refill, then again a few weeks into a new plaster cure, and keep calcium hardness and total alkalinity in range.
• Watch pH on the edge. Because the spill outgasses CO2, pools with a negative edge tend to drift upward on pH; testing more often than you would for a plain pool catches it.
• Wipe the edge wall when the pump is off. A week of fresh deposit wipes away; a summer of it does not.
• Partially drain and refill when hardness climbs late in the season.

We work negative edge pools in Chandler, Ocotillo, Ahwatukee, Gilbert, Sun Lakes and Tempe.