Pool Chemical Balance and Cover Selection Before Closing Day

The most common complaint I hear from pool owners about spring opening is the state of the water. Green, algae-heavy water after a winter closure happens for a specific reason: the chemical balance was off when the pool was closed, and six months of no maintenance let whatever imbalance existed amplify unchecked. Getting the chemistry right in October prevents two days of shocking and treating in May.

The chemistry sequence before closing

Test the water one to two weeks before your planned closing date, not on closing day. This gives you time to make corrections and let the water stabilize before you add closing chemicals. The targets are: pH between 7.2 and 7.6; alkalinity between 80 and 120 ppm; calcium hardness between 180 and 220 ppm. A pool water test kit with strips or a digital reader handles all three measurements.

High pH drives calcium precipitation, which creates scale on pool surfaces and equipment. Low pH etches plaster and irritates eyes. Both create conditions where algae can establish more easily during the low-maintenance winter months. Adjust these before adding winterizing chemicals — the winterizing treatments assume a balanced starting point and won't fully compensate for a pool that's already out of range.

The closing chemical sequence

A pool winterizing kit typically contains an algaecide, a sequestrant (which binds metals and prevents staining), and a slow-dissolving chlorine treatment designed to persist through the winter. Add these according to the kit instructions — usually with the pump running to distribute the chemicals, then run the pump for another twelve to twenty-four hours before covering.

Shocking the pool the week before closing with a standard non-stabilized chlorine shock gives the closing algaecide a clean starting point. Starting with low sanitizer levels and then applying algaecide is less effective than applying algaecide to an already-shocked pool.

The cover decision

There are three main options for pool covers: standard winter covers (essentially a tarp with anchors), safety covers (mesh or solid, anchored into the deck with hardware), and automatic covers. The standard tarp cover is the cheapest but also the most work to maintain through winter — it collects standing water and debris, and the water pumping is a recurring task. A solid pool safety cover with deck anchors stays taut, prevents debris accumulation, and prevents accidental falls.

For above-ground pools, the cover is typically held down with a water tube ring or cable-and-winch system. The float pillow that goes under the cover before closing serves a structural purpose: ice exerts outward pressure on pool walls as it expands, and the pillow gives the ice somewhere to push that isn't the pool wall. Don't skip it on above-ground pools.

What I'd skip

Skip chlorine and bromine tablets in any in-line chemical feeder when closing. Leaving these chemicals concentrated in a feeder against the walls of a closed pool for six months will bleach, etch, or damage the feeder and the surrounding plumbing. Empty all feeders completely before closing. Also skip the idea of not lowering the water level if you have tile or stone coping at the waterline — ice expansion against hard surfaces cracks grout and pops tiles. Four to six inches below the skimmer opening is the standard recommendation for tile-lined pools.