Frequently asked questions about pool maintenance

The recommended range is 7.2 to 7.6; the regulations that apply in the Madrid region (RD 742/2013) allow 7.2 to 8.0. It's the parameter that has the biggest knock-on effect on everything else, with unbalanced pH, chlorine barely disinfects. We cover it in detail in our guide on pH: how to raise or lower it.

They're chlorine that has already combined with organic matter and stopped disinfecting. Free chlorine, the kind that actually works, barely smells at all, a strong smell is a sign of chloramines, not excess chlorine. More in our guide to chlorine smell.

Always because of algae. It's fixed first by correcting the pH and then with shock chlorination, you almost never need to drain the pool. Full guide in green water: what to do.

A number that combines pH, temperature, calcium hardness and alkalinity to tell you whether the water is corrosive, balanced or scale-forming. You can calculate it with our Langelier Index calculator.

Never. It can generate chlorine gas, which is toxic if inhaled. Each product must be handled and stored separately, we explain it in safe storage of chemical products.

As a rough guide, every 5-7 years, depending on use. If the water comes out cloudy despite correct chemistry, the sand is usually the first suspect. Detail in filter sand replacement.

With the bucket test: you compare how much a bucket of pool water drops against how much the pool itself drops over 24 hours. If the pool drops noticeably more, there's a leak. Explained in water leaks: how to detect them.

It depends on your pool: it pays off in medium or large pools that get dirty regularly, and less so in small pools with little dirt. It doesn't replace chemical treatment. More in robotic cleaner vs. manual cleaning.

From most to least filtration power: diatomaceous earth, cartridge, zeolite, recycled glass and silica sand. Full comparison in filter types.

Only testing the water once it already looks bad. By then the imbalance has been building for days. We go over the most common ones in common maintenance mistakes.

Yes, it's a legal requirement for pools open to public or collective use, not something optional. We cover it in a safe pool for the family.

No, they give a false sense of security. Real safety combines physical barriers, active supervision and preparation; none of them is enough on its own.

Not a good idea without checking their compatibility first. Pool products should never be mixed or share a dosing unit with each other, detail in safe storage.

There's no fixed date, it depends on the weather, but the process always starts by carefully removing the cover and running the filtration for 24-72h before the first swim. Full guide in season opening.

It's no longer mandatory in the Comunidad de Madrid, Decreto 99/2024 allows you to keep the water during closure as long as its quality is guaranteed on reopening. More in Decreto 99/2024.

It cuts evaporation by up to 95-98%, which saves water and chemicals, and protects chlorine from the sun. Detail in thermal pool cover: what it's for.

Three checks: initial (pre-opening), routine (daily) and periodic (monthly), plus a Sanitary Control Record Book. Full guide in RD 742/2013 regulations.

More water checks (an initial test in the fortnight before opening and at least one a month; turbidity measured with kits meeting UNE-EN ISO 7027-1) and health staff at pools over 500 m² (except communities of up to 30 homes). It replaces the old Decreto 80/1998. Detail in Decreto 99/2024.

Yes, from 2 January 2027, for pools open to public or collective use. We explain it in professional certificate 2027.