Why draining is the wrong first move
It is treated as the obvious reset for a neglected pool, and it carries real risks that are expensive and sometimes permanent:
- A vinyl liner can shrink and will often not go back. Liners are held in shape by water pressure; empty one in warm weather and it contracts. Refilling can leave it permanently wrinkled or short of the track.
- A fiberglass or concrete shell can float. An empty shell with high groundwater behind it is a boat. Hydrostatic uplift lifts and cracks pools, and this is not a rare failure.
- Plaster can craze and crack. Exposed plaster dries unevenly in sun and wind.
- You dump a lot of treated water, which may also be restricted where you live. The EPA’s WaterSense program is worth a look on the water-use side.
- Refilling and rebalancing costs money and takes days.
The recovery sequence, water in
- Remove bulk debris first, mechanically. Leaf rake across the surface, then across the floor in sweeps toward the shallow end. Do not start with a robot — a carpet of leaves fills its basket in one lap. The leaf guide covers the technique.
- Clean your skimmer and pump baskets, and the filter. Start with circulation actually working, not nominally working.
- Test and balance. pH first, then alkalinity. Shock chemistry does not work outside a sane range, so this is not an optional step. Use the CDC’s target ranges as the reference.
- Brush every surface by hand — walls, floor, steps, behind the ladder, light niches. This breaks the biofilm so the sanitizer can reach the algae beneath it. Skipping this is why shocks fail.
- Shock, per the product’s own dosing. Take your robot out first.
- Run circulation continuously — 24 hours or more. This is the one phase where long pump run-time is genuinely warranted.
- Once chlorine falls back toward normal, run a fine-filter cleaner repeatedly as the water clears. Dead algae is a few microns across; a coarse basket passes it entirely. The algae roundup covers the filtration side.
- Add a flocculant if it is still cloudy after a couple of days, then remove the settled material.
- Rebalance, and only then swim.
Partial draining, which is sometimes right
Draining a portion — a third, say — is a different proposition and is genuinely useful for diluting high stabilizer (cyanuric acid), high calcium hardness or high total dissolved solids, none of which can be chemically removed. Keep enough water in to maintain pressure on the liner or shell and you avoid the structural risks.
When a full drain is genuinely necessary
- Replacing a liner.
- Structural repair to the shell or plaster resurfacing.
- Water chemistry so far out that partial dilution cannot reach a usable range — a real but uncommon situation.
In every one of those cases, it is a job for a pool professional who will check groundwater and use a hydrostatic relief valve. It is not a DIY weekend.
The honest expectation
A badly neglected pool recovered without draining takes three to seven days of circulation, filtering and repeated cleaner cycles. It is slower than a drain-and-refill and dramatically cheaper and safer. The main thing it asks of you is filter maintenance — you will be rinsing a fine filter after every single cycle, and that is the work.
