Filter, pump, run time: the equipment behind clear water

Reaching for chemicals when the water goes cloudy usually means treating a filter problem with a disinfectant. That rarely works and it is expensive.

Pool equipment runs quietly in the background until it stops. Which is exactly why it repays a little understanding.

Backwashing: by pressure, not by calendar

A sand filter does not get cleaner the more often you backwash it – rather the opposite. A lightly loaded filter filters more finely than a freshly cleaned one, because the trapped dirt acts as an additional layer.

The right moment is written on the pressure gauge. Note the pressure once with a freshly backwashed filter and empty baskets: that is your baseline. When pressure rises roughly 0.3 to 0.5 bar above it, backwashing is due.

Without that baseline the reading is a number without meaning. With it, it is the most reliable statement the system makes about itself.

• Switch the pump off first. Valves are never turned under pressure.
• Backwash until the sight glass runs clear – usually one to two minutes.
• Then rinse briefly so that the sand bed settles again.
• Check the water level: backwashing uses a noticeable amount of water.

If pressure suddenly falls instead of rising, that is not good news. Usually the pump is drawing air, a basket is blocked or the suction line is leaking.

Sand on the floor of the pool

Fine sand on the pool floor, in cones beneath the return jets, almost always means something inside the filter has failed – usually a cracked lateral or a split standpipe.

Carrying on does not help. The sand bed loses material, filtration drops off, and the sand ends up in the pump and the pool.

When the sand needs changing

Filter sand wears out. Over the years the grains round off, bind together with grease, sun cream and scale, and barely filter at all. As a rule of thumb, expect a change every five to seven years – on Mallorca towards the lower end, because hard water and a long season are harder on it.

Signs of exhausted sand: the water stays cloudy although the readings are right; pressure climbs again immediately after backwashing; and on opening the filter you find clumps rather than loose grains.

Run time: turnover, not guesswork

Filter run time follows the volume of the pool, not a feeling. As a guide, the entire contents should pass through the filter at least twice a day, and more in peak season or with heavy use.

The hours follow from pool volume divided by pump flow, multiplied by the number of turnovers. With a variable-speed pump it is almost always better to run longer and slower than short and fast: the filter works more finely and consumption drops sharply.

When you filter matters too. The main run belongs in the warm hours when the pool is in use and demand is highest – not overnight because electricity is cheaper.

What the pump tells you

• A grinding or singing noise: suspect a failing bearing. It almost always announces itself weeks in advance.
• A rattle like gravel: often cavitation – the pump is not getting enough water. Check the strainer, the skimmer basket and the suction line.
• Dripping between motor and pump housing: the mechanical seal is leaking. Left alone, water eventually reaches the motor bearing.
• A strainer pot that never fills completely: air in the system, a leaking lid or a perished O-ring. A dry lid O-ring is the most common and cheapest cause.
• A pump that shuts itself down: often overheating from poor plant room ventilation or from a suction side that is throttled too far.

The lid O-ring wants greasing – with silicone grease, not petroleum jelly. It is a two-minute job that prevents a great many air problems from arising at all.

Saltwater chlorination: the scale sits on the cell

Saltwater systems are convenient but ask for one extra piece of attention: in hard water, scale builds on the plates of the cell and throttles chlorine production.

Many cells clean themselves by reversing polarity, though with Mallorcan water that is often not enough on its own. A look inside the cell once a season quickly shows whether more is needed. And pH needs particular attention here, because electrolysis drives it upwards by design.

The short round that always pays

• Read the pressure gauge and compare it with the baseline.
• Empty the skimmer baskets and the pump strainer.
• Listen for noises and look for moisture under the pump.
• Check the water level – too low and the pump draws air.
• On dosing systems, check the supply and the tubing for leaks.
• Write down the readings and anything unusual, with the date.