Common questions on pool care and Pool Buddy

During the swimming season, at least twice a week; with lots of sun or daily use, every 1–2 days is better. After heavy rain, shock treatment or pool parties, retest immediately.

Best time: morning before sun exposure – readings are most meaningful then.

Free chlorine: 0.3 to 0.6 mg/l · Combined chlorine: below 0.2 mg/l · Total chlorine: below 1.0 mg/l.

From 1.5 mg/l free chlorine sensitive swimmers may react; above 3.0 mg/l counts as too high – see Chlorine too high: safely lower it.

7.0 to 7.4. Within this range chlorine works at about 70 percent efficiency, calcium does not precipitate, and the water does not irritate skin. Above 7.6, chlorine loses up to 80 percent of its efficacy.

Details and dosing guide: Pool pH level done right.

Target range: 80 to 120 mg/l. Alkalinity acts as a buffer for pH – if it's too low, pH bounces with every dose ("pH bounce"). Testing alkalinity once a month is usually enough.

Cyanuric acid (also called stabiliser or "chlorine sunscreen") protects free chlorine from UV degradation. Target range: 20 to 40 mg/l. Above 60 mg/l chlorine becomes increasingly ineffective – then only a partial water change helps.

Too low? How to raise CYA: Either deliberately with pure stabiliser (cyanuric acid granules) – add slowly via the skimmer, circulate for 24 hours, then re-test. Or as a side effect of stabilised chlorine granules (dichlor/trichlor), which add CYA with every dose. Pure stabiliser is easier to control, because CYA cannot be filtered out – the only way down is a partial water change. The app calculates the exact amount for your pool volume.

In 80 percent of cases pH is too high – chlorine can barely work and calcium falls out of solution. Second most common cause: clogged or under-backwashed filter. Third: low free chlorine combined with high cyanuric acid (above 60 mg/l).

Full diagnosis: Cloudy pool water – causes and fix.

In this order:

1. Lower pH to 7.0–7.2. 2. Shock with 20–40 g of chlorine granulate per m³. 3. Run the filter continuously for 24–48 hours. 4. Vacuum out the dead algae.

Important: get the filter running before adding chlorine. Detailed guide: Green pool – killing algae.

The pungent "chlorine smell" does not come from free chlorine but from combined chlorine – chlorine that has already reacted with body oils, sunscreen and urine. A clean, well-chlorinated pool barely smells.

Fix: a shock treatment oxidises the combined chlorine and clears the smell.

Brown discoloration usually means iron in the fill water (well water). Fix: add a metal remover (sequestrant) and adjust pH to 7.2.

Yellow film on the walls is often mustard algae – tougher than green algae, needs a higher shock dose (30–50 g/m³) and thorough brushing of all surfaces.

No. Pool Buddy is fully free – no account, no subscription, no ads. Funded through voluntary Ko-fi donations.

No. All readings, pool sizes and dosing histories stay exclusively on your device. There is no server, no cloud sync and no user accounts. The app works completely offline.

Yes. Pool Buddy is a Progressive Web App (PWA) and runs in any modern browser. On Android and iOS you can install it via "Add to home screen" from the browser menu – it then behaves like a native app, offline usage included.

Yes. Pool Buddy supports multiple pool profiles with different volumes, filter runtimes and target values – useful for landlords, property managers or tracking a main pool and a kids' pool separately.

Settings offer an "Export data" option. The app writes a JSON file that you can transfer to the new device via e-mail, cloud storage or cable, then import there.

For daily baseline sanitation, 2–3 g of free chlorine per m³ per week via tablets is enough (so 40–60 g per week for 20 m³). For a shock treatment use 20–40 g of chlorine granulate per m³, i.e. 400–800 g.

The app calculates exact amounts from your current chlorine reading and measured cyanuric acid.

After a normal dose, immediately, once the value settles at 0.3–0.6 mg/l free chlorine. After a shock treatment, only once the value has dropped below 1.0 mg/l – usually 24 to 48 hours.

Always retest, never guess. Details: Chlorine too high: safely lower it.

No. Always leave at least 2 hours between them, with the filter running. Directly mixing them can release chlorine gas – dangerous to airways and damaging to your pool equipment.

Dry, cool (below 25 °C), light-protected and separated: chlorine products, pH regulators and algaecides must never come into contact with each other – not even through spilled powder. Keep away from children and pets. Store chlorine tablets in the original packaging, not in shared containers.

It depends on the pool material and how hard the winter is.

• Liner frame pools (Bestway Steel Pro Max, many Intex models): In frost-prone regions, take them down. The PVC liner becomes brittle at frost temperatures and ice pressure deforms the steel frame. Empty the pool, dry the liner and store it folded in a frost-free place.
• Steel-wall above-ground pools: Can usually overwinter outside. Lower the water level substantially, add ice compensators, fully drain the technical system and store it frost-free, then cover tightly. In extreme frost or without a proper winter cover, take it down to be safe.
• Permanently installed pools (in-ground liner, concrete, GRP): Stay in place. Lower water below skimmer/return jets, fully drain pipes and pump, add winter chemistry, cover tightly.

When in doubt, follow the manufacturer's instructions. Pool Buddy's guided winterizing checklist walks you through the steps and gives a specific recommendation based on your setup.