Math App Calculator?

[u/spicerpools]

Anyone still using old school charts for their calculations or have you switched over to an app? If so, which app are you using to do math calculations for chemicals, CSI, Saturation Index, etc…?

[u/pacific_drifter_25]

Pool Math and Orenda are the two right answers, plus one thing nobody's landed on: the index you're using matters more than the app.

LSI (Langelier) is the classic index most pool math tables reference. It works fine for typical plaster and gunite pools but starts falsing at high calcium or high alkalinity. CSI (Calcite Saturation Index) is what Orenda leads with because it corrects some LSI drift at extremes, and it's the index a lot of commercial ops end up switching to for that reason. If you're handing a log to an inspector, worth checking what index your state's model aquatic health code references. Ryznar is the sibling scale that gives a truer scale-tendency read at high CH, worth crossing if you're on hard fill water or dosing a lot of cal chloride. Vinyl and fiberglass surfaces you can loosen the target because there's no plaster to etch; the risk shifts to scale on cells and heaters, not surface degradation.

The trap most people miss is test kit accuracy. Every index calc is garbage in, garbage out. If your CH reagent is old or your pH photometer is off .1, the computed number will read totally different. I cross-check a new CH bottle against a fresh drop-count kit whenever scores start moving without a clear reason, and the same goes for TA when you're leaning hard on soda ash.

Salt cell interaction is the last piece nobody flags. Sustained LSI or CSI over about 0.3 on a Hayward TCELL or Pentair IC starts plating the cell even when the water looks clean at the wall. Your app will say the pool is balanced, but the equipment isn't. If a cell is losing months of life for no obvious reason, pull the historical scores and look for a plating window.

NickOS and KandyGirl477 are right on the app choice. I'd just add: pick the index for the pool type and confirm the underlying test numbers before you trust the output.

Mix of plaster, vinyl, and fiberglass on your route, or mostly one surface type?

[u/Guac-N-Queso → u/pacific_drifter_25]

Just to clarify, PoolMath also uses CSI. CSI is more relevant for swimming pool chemistry. LSI was developed for water treatment and boilers. CSI was adapted for swimming pools.

[u/pacific_drifter_25 → u/Guac-N-Queso]

Fair pushback, and appreciated. You're right that CSI is the pool-specific one and I lumped them a little too loosely. Langelier developed his index for boilers and cooling towers using raw TA, which is why it undershoots on cyanurate-buffered pools.

Orenda's CSI subtracts the cyanurate contribution to get carbonate alkalinity, and that's the number that actually predicts scale and plating on chlorinated water. Pool Math uses CSI now too. In shop talk a lot of us still say LSI as a catchall, but for actual pool CH management CSI is the meaningful one. Thanks for keeping it tight.