Hot tub filter cleaning and replacement: a practical guide

The filter is the quiet worker of your hot tub: you do not see it or hear it, but every time you get in, it decides whether the water is crystal clear and pleasant. If you clean it regularly and replace it in time, you will need fewer chemicals, the pumps will work more easily, and you will need to change the water less often. In this guide we go through how often and how to clean it, when it has reached the end of its life, how to find the right replacement, and what to do with the filter if you have just bought a used hot tub.

Why does the filter matter so much?

The filter catches the dirt floating in the water: hairs, tiny particles shed from skin, greasy residues from skin and body care products, dust and bits of leaves. The sanitiser (chlorine, bromine or active oxygen) deals with germs, and the filter deals with solid dirt. Together they give you clean water.

A clogged filter comes back to bite you in several ways:

• Cloudy, dull water that chemicals do not really fix.
• Weaker jets, because water has a harder time passing through the filter.
• More strain on the pump, which in the long run also shortens the life of the equipment.
• More chemicals, because the dirt trapped in the filter keeps using up the sanitiser.

How often should you clean the filter?

Rinse it every week or two depending on use (and at least once a month), and clean it thoroughly by soaking it in filter cleaner, typically every one to three months and at every water change. Manufacturers' recommendations fall within this range, so your own hot tub's owner's manual is the reference.

If many of you bathe often, or you get in with sunscreen on your skin in summer, clean it more often. If the hot tub is barely used for weeks, less often is enough.

How do you give the filter a quick rinse?

For a quick rinse, all you need is a garden hose with a plain, straight-jet nozzle and ten minutes.

1. Switch off the hot tub at the main isolator or the circuit breaker.
2. Remove floating leaves and debris from the filter housing before lifting out the filter, so they do not get into the pipes.
3. Lift or unscrew the filter as described in the manual.
4. Working from top to bottom, spray water between the pleats at about 45 degrees, turning the filter as you go, until every pleat is clean.
5. Put it back, but do not overtighten screw-in filters.

How do you deep clean it, step by step?

The key to a deep clean is soaking the filter in filter cleaner, because plain water does not dissolve greasy, oily deposits and limescale.

1. Switch off the power. Switch off the hot tub at the main isolator or the circuit breaker.
2. Take out the filter. First remove the debris floating in the filter housing, then lift out the filter.
3. Rinse it. With a garden hose, at 45 degrees, between the pleats, from top to bottom, turning the filter.
4. Soak it in filter cleaner. In a clean bucket, with a cleaner made specifically for hot tub filters (for example AquaFinesse Filter Cleaner tablets), at the dose and for the time given on the label. For many products, overnight works best. The filter should be fully submerged.
5. Rinse it again, very thoroughly. Keep rinsing until no foam or cleaner residue comes out. Leftover cleaner can cause foaming and water chemistry problems in the hot tub.
6. Let it dry. Let it air dry in a shaded, well-ventilated place, without direct heat. Many filter makers recommend letting it dry completely, which is also good for the fibres.
7. Check it and put it back. Check the pleats, the end caps and the sealing ring, then put the filter back. Do not overtighten a screw-in filter.

Why is it worth keeping a spare filter?

Because then the hot tub is never out of action: while one filter soaks and dries, the other one works. Filter makers and hot tub manufacturers both recommend this rotation.

• The filter can dry out completely at its own pace, with no need to put it back in a hurry while still wet.
• The two filters share the load, so both last longer.
• If one gets damaged, you are not left without a filter.

How do you know the filter needs replacing?

It needs replacing when even a deep clean no longer makes it clean and intact again, or when the water stays cloudy despite correct water chemistry. Watch for these signs:

• Torn, frayed filter material. Water passes through the tear without being filtered.
• Flattened, matted, collapsed pleats. Such a filter has a much smaller surface area than a new one.
• A cracked, brittle, crumbling end cap, or pleats that have come away from the end cap. Here the water bypasses the filter material.
• Hard, stiff pleats coated with limescale. The mineral deposits stiffen the fibres, and cleaning no longer dissolves them.
• Permanent discolouration. If it stays brown, grey, greenish or dark yellow even after cleaning.
• Cleanliness lasts less and less. If a freshly cleaned filter clogs again within a few days, the jets weaken or the water stays cloudy, the filter is worn out.

How long does a filter last?

The replacement interval given by manufacturers is typically 1-2 years, and for the original filters of some premium manufacturers up to 3 years with careful maintenance. The actual life depends on how often the hot tub is used, the water hardness, the water care and how regularly the filter is cleaned, so look at the condition of the filter, not just the calendar. You will find the exact recommendation in the documentation from your hot tub or filter manufacturer.

If your hot tub has several filters, it is worth replacing them all at once so that they work evenly.

How do you find the right replacement filter?

The surest route is the exact details of the old filter: the part number on the end cap, plus the length, outer diameter, centre hole and the design of both ends. With a used hot tub, where you do not know what was in it before, these four steps help:

1. Find the part number

On most filters the manufacturer's part number is moulded or printed on the end cap. If it is still legible, this is the quickest starting point: the cross-reference tables of the large aftermarket makers (for example Pleatco, Unicel or Darlly) list the compatible types.

2. Check the brand and model of the hot tub

The make and model of the hot tub (from the manual, the rating plate with the serial number or the inside of the service panel) help a lot, because manufacturers typically specify the filter per model. Some brands use their own filters that are only available from them.

3. Measure the filter

Measure in millimetres. An old filter can shrink or expand slightly over time, so a difference of a few millimetres from the catalogue data is still acceptable.

4. Check the design of both ends

• Top: open hole, closed top, handle or removable lid.
• Bottom: open hole or thread. The thread can be fine (6-8 thin turns) or coarse (about 3 thicker turns). Even in Europe, manufacturers typically give thread sizes in inches (for example 1½ or 2 inch).

What should you do with the filter if you have just bought a used hot tub?

Start with a new filter. You cannot know how the old one was cleaned or what water it worked in, and the price of a new filter is small next to the value of a clean start.

1. Identify the old filter with the steps above and get a new one (one for each filter position if there are several).
2. Flush the pipework following the line flush product's instructions, then drain and clean the hot tub.
3. Refill with fresh water, and only then fit the new filter, so that it does not catch the old deposits on day one.
4. If the old filter is intact, you can deep clean it and keep it as a spare, but if it shows any of the replacement signs above, do not hesitate to throw it away.

That way your hot tub really does get a clean start with you, and in the first weeks you will also experience what the water is like when everything is in its place.