Sep 8, 2026 · 36 min · 13 segments
Eight real questions this episode, pulled from the Ask John page, the Trouble Free Pool forums, and real clients of the Pools Scientific field lab. Every one of them starts the same way: a reading…
He has a plaster pool with a salt system with an infinity edge, and for two years running he's been getting these sharp little calcium crystals on the plaster walls.
pH is at 8.0, alkalinity is at 75, calcium hardness is at 280, CYA at 20, and salt around 3200.
And the app he's using told him that his LSI was a positive 0.04 right when he tested it.
So he asked me, If the number is that close to perfect, why is this scale still showing up on my walls? The first thing worth clearing up is that 280 parts per million calcium isn't low for a plaster pool.
So this was never a calcium leaching out of the plaster problem in the first place.
What he's looking at is scale forming on top of it, which is a completely different problem with a completely different cause.
It's a kinetic thing, more like a running total than a light switch you just flip on or off.
Mike tests roughly once a week, and in the days between tests, his infinity edge and his salt cell are both pushing pH up at the same time.
The edge is off-gassing carbon dioxide on one side, and the cell is doing its own local pH thing on the other.
And by his own account, LSI on that pool has climbed as high as 0.4 during that stretch between corrections, which isn't really a rounding error.
It's a real sustained oversaturation sitting there depositing calcium carbonate the entire time.
And then, by the time he tests it again, it's already settled back down near balanced, like nothing ever even happened.
It also explains those two quiet years because that buffing and acid wash left a genuinely smooth surface.
And smooth surfaces just don't give new calcium carbonate crystals anywhere easy to grab onto.
He has a plaster pool with a salt system with an infinity edge, and for two years running he's been getting these sharp little calcium crystals on the plaster walls.
pH is at 8.0, alkalinity is at 75, calcium hardness is at 280, CYA at 20, and salt around 3200.
And the app he's using told him that his LSI was a positive 0.04 right when he tested it.
So he asked me, If the number is that close to perfect, why is this scale still showing up on my walls? The first thing worth clearing up is that 280 parts per million calcium isn't low for a plaster pool.
So this was never a calcium leaching out of the plaster problem in the first place.
What he's looking at is scale forming on top of it, which is a completely different problem with a completely different cause.
It's a kinetic thing, more like a running total than a light switch you just flip on or off.
Mike tests roughly once a week, and in the days between tests, his infinity edge and his salt cell are both pushing pH up at the same time.
The edge is off-gassing carbon dioxide on one side, and the cell is doing its own local pH thing on the other.
And by his own account, LSI on that pool has climbed as high as 0.4 during that stretch between corrections, which isn't really a rounding error.
It's a real sustained oversaturation sitting there depositing calcium carbonate the entire time.
And then, by the time he tests it again, it's already settled back down near balanced, like nothing ever even happened.
It also explains those two quiet years because that buffing and acid wash left a genuinely smooth surface.
And smooth surfaces just don't give new calcium carbonate crystals anywhere easy to grab onto.
Every episode on Radar is fully transcribed, speaker-labeled, and rich with metadata. Here is a taste of this one. Try Radar for free to see the rest.
The rest of this transcript — segmented and speaker-labeled, so you land on the exact moment something was said
All 13 segments — the transcript broken into labeled sections, every ad read marked
All 25 topics — jump to every other episode discussing the same subject
Every related episode — other shows Radar links to this one
No account is needed to search Radar.
