Balance or Bust: Finding the Ideal pH with Eric Knight

We opened with a challenge to pool care dogma: stop chasing a tight 7.4 to 7.6 pH in outdoor pools when cyanuric acid is the stronger variable controlling chlorine’s active strength. The eye-pH claim doesn’t hold water, and we cite sources beyond casual references to show that eyes vary widely and cannot reliably “feel” pH. What matters more is how stabilizer binds chlorine, how that binding lowers the fraction of hypochlorous acid, and how ratio thinking outperforms rigid set points. When CYA is elevated, chlorine’s bite is dulled, regardless of whether the pH is 7.4 or 7.8, and that realization frees operators from the weekly acid yo-yo that harms LSI and surfaces while delivering little sanitation benefit.

From there we quantify what “ratio thinking” looks like. Drawing on committee work and Richard Falk’s modeling, we explain why the CYA-to-free chlorine ratio should not exceed 20:1, and why many pools do better keeping stabilizer near 30 to 50 ppm to balance UV shielding with usable chlorine. If you run CYA at 100 ppm, you may need to carry 7.5 ppm free chlorine just to stay ahead of algae, which raises costs and risk of byproducts. Lower CYA means faster working chlorine and fewer surprise blooms, even if you dose more often. We also clarify that indoor pools with no CYA revert to classic chemistry—there, pH directly steers chlorine strength, so the old rule applies, but outdoors it gets overpowered by stabilizer.

We then confront the practical fallout of obsessive pH correction: acid overuse. Most techs overestimate the acid needed to move pH from 8.0 to 7.5 in a 20,000-gallon pool, often dumping a half gallon to a gallon when a quart would suffice, depending on alkalinity. That mistake slams the LSI, risks localized etching where acid plunges, and opens up surfaces to oxidation and fading. We outline better technique: measure, calculate, and pre-dilute acid to avoid hot spots. The goal is stable water on the Langelier Saturation Index, minimizing swings instead of “resetting” pH to a narrow band that will rebound within days.

Alkalinity becomes the next lever. It’s the buffer that dictates how much acid is required for a given pH move, and it includes bicarbonate, carbonate, and cyanurate components. The higher the alkalinity, the more acid you must “burn through” to achieve the same pH drop. We also note borates and even phosphates contribute modestly to buffering. However, the overlooked stabilizer of LSI is calcium hardness. Because calcium doesn’t drift rapidly, it anchors your saturation balance like an antacid, allowing pH and alkalinity to breathe without sending LSI on a roller coaster. By elevating calcium into a healthy range and tuning alkalinity thoughtfully, you gain a calmer, more predictable system.

Finally, we address the “pH bounce.” Many blame alkalinity for rapid rebounds, but poor acid application is the usual culprit. When undiluted acid streaks to the floor, it can etch plaster, pull high-pH calcium hydroxide into solution, and kick pH and LSI back up. Proper dosing, circulation, and patience solve more than brute force ever will. The big takeaway is simple: set CYA with intention, obey the FC-to-CYA ratio, protect your LSI, and use acid as a scalpel, not a sledgehammer. Fewer algae calls, fewer surface problems, and steadier chlorine performance follow when you stop fighting pH and start balancing the whole system.