Hot Tub Filtration Cycles: Should I Leave My Filter on All the Time?

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Hot tub filters have an important job: catching hair, bathing suit fibers, dirt or any other debris that makes its way into your spa—and preventing it from getting into the equipment where it can cause damage.

Your hot tub likely has several options for how often to run its filtration cycle. But how do you know which one to pick? 4 hours? 12 hours? Continuously?

Most residential spa owners do not need to run their hot tub pumps all the time. Unless the spa is used multiple times per day, a filtration cycle of 2-8 hours, twice a day, should be enough to keep most hot tubs sanitary.

Let's take a look at filtration cycles in more detail, and find out how you can determine the right schedule for your spa.

What are hot tub filtration cycles?

Filtration cycles are periods of time when hot tub pumps are scheduled to run automatically, circulating water and chemicals through the filter system and pipes—regardless of whether the spa is in use or not.

A hot tub full of standing water is the perfect breeding ground for bacteria.

That's why it's important to circulate hot tub water on a regular schedule; to filter out any contaminants before they have the chance to make your water unsanitary.

How often should you run your pump?

As a general rule, you should aim for the shortest filtration cycle needed to maintain clean water in your hot tub. What this is will depend on your spa, usage and local water quality, and will need some experimentation to figure out initially.

Here are some starter guidelines based on usage:

  • A couple, occasional use: 2-hour cycle, twice per day
  • Small family, or couple who entertain regularly: 3 or 4-hour cycle, twice per day
  • Large family, frequent use, especially by kids: 6 or 8-hour cycle, twice per day

Many manufacturers recommend 8 or 12-hour cycles, but most spa owners I know find that to be unnecessary. Personally, my hot tub (used by two people) is just fine with 2-hour cycles running twice per day.

Pick a filtration cycle based on the usage guidelines above. If the water stays clean for a few weeks, reduce the filtration cycle time by an hour. Repeat until you start to notice cloudy water, or your sanitizer levels become hard to maintain.

When you might need to run your pump all the time

There are two situations where you might want to run a hot tub pump all the time.

Very heavy usage

The first is if you have incredibly heavy usage, to the point where none of the shorter cycles are able to keep the water clean.

I don't know of any case where this has been necessary, but I imagine it could be possible if the hot tub was being used multiple times a day, with dirt tracked in regularly, and other contaminants like drinks being spilled in the water.

You have a 24/7 circulation pump

Hot tubs can have different types of pump:

  • Most hot tubs just use a standard jet pump to circulate the water through the heater and filter. This pump is used to run the jets both when the tub is in use, and on low speed during filtration cycles.
  • A circulation pump is a smaller pump that, unlike jet pumps, is designed to be run continuously. The idea is that they are more energy efficient, offer 24/7 filtration, and are quieter while running.

There is some debate around whether circulation pumps are actually as beneficial as some manufacturers claim, but if your spa has one, know that it is intended for this pump to run all the time.

When is the best time to run hot tub filtration cycles?

By default, most hot tubs will start their filtration cycle at the time you first turn on the spa, and then run on a schedule every 12 hours after that.

Filter after use

To get the most benefit from the filtration, it makes sense to have a cycle run just after you usually use the tub. That's so any contaminants that made their way in can be cleaned up, and not left to sit in water for too long where they could attract bacteria.

So, if you're an evening spa user and usually like to soak between 7pm and 9pm, you could set your filtration cycles to run at 9pm and 9am.

Aim for off-peak hours

Many spa owners also time their cycles for off-peak hours, when energy is cheapest. Peak hours are usually 6am to 10am, and 5pm to 9pm.

So, a 4-hour cycle set to run at 11am and 11pm, for example, would avoid these hours (which could save on energy costs).

What happens if you don't run your filter enough?

The telltale signs that you're not filtering your spa water enough are:

  • You notice the water getting milky or cloudy
  • Your hot tub develops a 'pond' or algae-like smell
  • Sanitizer levels seem to drop quickly, and are hard to keep at the recommended level
  • Foam or biofilm (a creamy/green substance) appear on the surface or around the waterline of your spa

These are all signs of poor sanitation. If you see any of these, shock your tub, and increase the filtration cycle time. In severe cases, you may need to drain, clean and refill the tub with fresh water.

What happens if you run your filter too much?

If your filtration cycles are too long, you'll have a clean hot tub. However, you'll also be wasting energy, putting unnecessary strain on your pump, and your filters could need changing more regularly.

Over time, these things will all cost you more than if you'd experimented a little to find the most efficient filtration cycle for your particular hot tub and usage.

Should you leave your hot tub on all the time?

Independent from filtration cycles, you should definitely leave your spa connected to power and 'on' all the time.

Hot tubs are designed to be kept warm: it's actually more energy efficient to maintain the heat of a hot tub than to heat the water from cold for every use.

What's more, many of the chemicals used to maintain safe water need heat to work properly and maintain your water balance.

Should you ever run your hot tub without a filter?

You should never remove a spa filter for more than a few minutes at a time.

It's fine (and recommended) to take the filter out to rinse it every couple of weeks, but don't leave it out for longer than it takes to wash away debris with your garden hose.

And ideally, don't run the spa pump while the filter is out, or contaminants could get sucked into the equipment.

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