Quick facts
- Empty and refill: daily, with fresh water โ never top up a standing tank
- Full scrub: every 3 days in use
- Descale: weekly, white vinegar, roughly 30 minutes soaking
- Never: bleach left standing, and no part in the dishwasher
Empty and scrub the tank every three days. Descale it once a week. That is the whole schedule.
The reason it is that frequent is worth understanding, because it explains why people ignore it and regret it.
An ultrasonic humidifier sprays whatever is in the tank
These units vibrate a metal disc thousands of times a second and throw water off it as a fine mist.
The disc does not filter, boil or sterilise anything. It atomises what is there.
Bacteria, mineral scale and mould spores all leave the tank in that mist and end up in the air you are breathing.
A neglected ultrasonic humidifier is not a device that has stopped helping โ it is a device now distributing the problem.
Standing water at room temperature is a good enough culture medium after about seventy-two hours.
Hence three days, not a fortnight. It is a biology interval rather than a housekeeping one.
The pink or orange film that appears in tanks and around plugholes is usually Serratia marcescens, a common waterborne bacterium.
It is a reliable sign the tank has been left wet and untouched for too long.
Black or green spotting inside the reservoir is mould, and at that stage a rinse will not clear it.
The three-day scrub takes about ten minutes
Unplug it and take the tank off the base. Both parts need doing; most people only do the tank.
Tip out any water left in the tank and the base. Never top up over yesterday's water.
Wash the tank in warm water with a little washing-up liquid, and use a bottle brush on the corners.
The base is the part that matters most, because that is where the disc and the standing water live.
Wipe the transducer disc with a soft cloth or cotton bud, gently โ it is a component, not a surface.
Rinse everything twice, then leave the parts open to air-dry rather than towelling them shut.
A humidifier stored damp with the lid on is the one you will find mouldy in November.
White vinegar handles the scale that hard water leaves
Much of England, and the south-east in particular, has hard water.
That is dissolved calcium and magnesium, and it stays behind as a chalky crust on the disc and the tank walls.
Scale is the direct cause of the white dust ultrasonic owners find on nearby furniture.
For the weekly descale, fill the base with a solution of white vinegar and water and leave it for about 30 minutes.
Scale that has hardened over months may need an hour, and a second pass.
Loosen what remains with a soft brush. Never scrape the disc with anything metal.
Rinse thoroughly afterwards, because vinegar left in the base will be misted into the room along with everything else.
Using cooled boiled water, or filtered water, slows the scale down considerably. It does not remove the need to clean.
What not to do, and what the machine makes hard
Bleach is the usual mistake. A dilute solution briefly, then rinsed exhaustively, is defensible; bleach left to soak is not.
Nothing goes in the dishwasher. Neither the Levoit Classic 300S nor the LV600S has a single dishwasher-safe part, and that is typical.
The design of the machine decides how likely you are to keep this up.
RTINGS scores the Classic 300S at 6.0 for cleaning, helped by a wide tank opening on a 6-litre reservoir.
The LV600S scores 4.5, largely because it has close to twenty separate parts needing periodic washing.
Our Levoit LV600S review: the 5 numbers that decide it covers what that means in daily use.
If you are still choosing, count the parts and check whether your hand fits through the tank opening.
A humidifier you can clean in ten minutes is one you will clean. That is most of the decision.
