Bob Lowry on Surface Cautions Every Pool Pro Should Know

Choosing and caring for a pool surface is more than a design decision; it’s a chemistry and equipment strategy. Vinyl liners, fiberglass shells, plaster, and pebble finishes each respond differently to pH, alkalinity, chlorine, and circulation. We explore why vinyl and fiberglass often hold pH more steadily than plaster, why colored plaster can show mottling that chemistry alone won’t solve, and why pebble finishes invite calcium scale and algae into their crevices. By aligning water balance with the surface—rather than using one-size-fits-all targets—you reduce staining, etching, bleaching, and biofilm growth while extending the life of the finish.

Vinyl pools are budget-friendly and fast to install, but success starts beneath the liner. Proper ground prep prevents nutgrass from piercing vinyl, and a solid support structure keeps the membrane stable at the coping. Chemically, vinyl doesn’t feed alkalinity into water the way plaster does, so pH and total alkalinity need deliberate management. Keep calcium hardness around 200 to 250 ppm, not plaster-like levels; skipping calcium tests invites trouble when heaters or metal components enter the mix. Avoid acid contact with vinyl—single drops can bleach color instantly—while isolated trichlor tablets can also mark and degrade nearby surfaces. Gentle handling and consistent circulation protect vinyl’s thin barrier from tears, bleaching, and biofilm.

Fiberglass pools are surging thanks to rapid installs and smooth interiors, but they bring unique cautions. Many manufacturers void warranties when trichlor tablets are used in skimmers or floaters; a tablet left on a step can scar, stain, or blister gelcoat. Like vinyl, fiberglass doesn’t contribute alkalinity, so stable pH depends on measured dosing rather than surface buffering. Maintain moderate calcium hardness—enough to protect equipment, not enough to scale. Keep strong acids away from shells and fittings, and target steady sanitizer levels without spikes. When paired with efficient circulation and properly sized filters, fiberglass surfaces stay sleek, low-maintenance, and resistant to staining.

Plaster remains popular for its classic look, but it’s chemically active. Fresh plaster leaches alkalinity and calcium, altering pH and raising the pool’s acid demand. That reactivity means start-up care and ongoing balance matter: control pH drift, monitor alkalinity, and keep calcium hardness near 300 to 350 ppm to protect the matrix. Colored plaster can show mottling and trowel marks that stem from installation, not chemistry, so water care can’t fix every surface flaw. Still, balanced water minimizes etching, scaling, and discoloration risks. Think of plaster as a living surface: it rewards consistency, careful acid use, and patient start-up with long-term durability.

Pebble and exposed aggregate finishes trade smooth plaster for texture, which is attractive but can trap scale and algae. Diamond-polished versions reduce micro-crevices, yet maintenance still hinges on movement and brushing. Short filter cycles leave dead zones where sanitizer is depleted locally, letting algae take hold. Run circulation long enough for thorough turnover, add a robotic cleaner or brush once or twice weekly, and keep chlorine at levels that match stabilizer. Hard water raises the odds of calcium crust on pebbles; control pH, track carbonate saturation, and act early with mild descaling before deposits harden.

A pivotal tactic for all residential pools is matching free chlorine to cyanuric acid. Rather than chasing a flat 2 to 4 ppm, aim for 7.5% of CYA to reliably suppress algae. With 80 to 100 ppm CYA, that means about 6 to 7.5 ppm free chlorine, often higher than legacy charts suggest. If that sounds steep, add borates to 50 ppm. Borates are not an algaecide but an algistat, making it harder for blooms to start so you can slightly lower the required chlorine for the same protection. Pair this with prudent pH control and clean, continuous flow, and even pebble surfaces with deep texture stay clear.

Equipment matters as much as chemistry, especially for above-ground packages. Many ship with tiny cartridge filters, paper-like media, weak pumps, and no timers. Upgrading to a larger cartridge or sand filter, choosing a right-sized variable-speed pump, and adding a timer immediately improves clarity and chemical efficiency. Above-ground pools often lack a main drain, so surface-only suction leaves debris on the floor; robotic cleaners and routine brushing close that gap. Better filtration means fewer hours chasing chlorine loss, tighter pH control, and less scale and algae on any surface—vinyl, fiberglass, plaster, or pebble.