Calima is airborne dust, usually carried from North Africa, that coats cars, terraces and, of course, pool water. The good news: you almost never need to drain the pool. What you do need is to get the dust out without clogging the filter, and to replace the chlorine that has been used up.
Getting the mud out without clogging the filter
What Saharan dust does to the water
- Cloudiness: the dust is a very fine mineral material. The heavier part settles on the bottom; the finest part stays suspended and takes away the clarity.
- A clogged filter: if all that mud goes through the filter, it clogs quickly and the pressure gauge shoots up.
- Less chlorine: dirt comes in with the dust and chlorine has to deal with it, so free chlorine usually drops after a heavy episode.
If there is a dust warning
When the forecast announces calima or "muddy rain", what helps most is to cover the pool with its cover or thermal blanket, if you have one. Every bit of dust that stays on the cover is dust you won't have to remove from the water. Take it off carefully so what has built up doesn't fall in.
After the dust, step by step
- Don't switch on the robot or vacuum to the filter with a muddy bottom: you'd send everything to the filter at once.
- Remove anything floating with a skimming net and empty the skimmer baskets and the pump pre-filter.
- Let it settle. With the pump off for a few hours (ideally overnight), the dust sinks to the bottom.
- Vacuum the bottom with the multiport valve on "waste" (or "drain"): the mud goes straight out without passing through the filter. Go slowly so you don't stir up a cloud. You'll lose some water; top it up afterwards.
- Backwash and rinse the filter to clear what it has trapped.
- Test pH and free chlorine and correct them. If chlorine has crashed or the water starts turning green, it's time for a shock treatment.
- Filter continuously for 24-48 hours and check again.
What if it's still cloudy?
If the water still lacks sparkle after one or two days of filtration, the particles are too fine for the filter. That's what clumping products are for:
- Flocculant: binds particles into clumps that sink to the bottom. It's used with sand or glass filters, with the pump off after spreading it, and the bottom is then vacuumed to waste again.
- Clarifier: groups particles so the filter can trap them. It's gentler and the option to choose if you have a cartridge filter.
Always follow the dose on the label for your pool's volume (if you're not sure, use the volume calculator).
Frequently asked questions
Do I need to drain the pool after Saharan dust?
Almost never. By vacuuming the bottom to waste, cleaning the filter and correcting chlorine, the water recovers in one or two days. Draining wastes a lot of water and, at certain times of year, can damage the pool shell.
Can I swim in cloudy water?
Better not. Besides not being able to see the bottom properly, which is a risk, chlorine is usually low after the episode. Wait until the water is clear and pH and chlorine are back in range.
Why has the filter pressure shot up?
Because the dust has clogged it. Backwash and rinse. If it rises again straight away, repeat, and next time vacuum the mud to waste instead of sending it through the filter.