This blog is about swimming pools, spas and hot tubs and how to maintain them.

Step-by-Step Guide to Replacing your Hot Tub Filter Cartridge


Trying to find a replacement filter cartridge for your spa or hot tub can be an arduous task due to the number of filters currently on the market. Not only are there different filters for different manufacturers but there are also different filters for different models by the same manufacturer! We hope that this blog post will help you find the filter that you are looking for.

The first thing you need to do when finding a replacement hot tub filter is to have your old filter to hand. Once you have it there are several ways in which you can identify the filter you need.

Reference Number

When searching for a replacement filter cartridge you will normally come across four main manufacturers which are Darlly, Filbur, Pleatco and Unicel. If you look on the top of your old filter most manufacturers of filter cartridges will state the manufacturers name and the filter code. These two bits of information can then be used to find your filter.


If you cannot find a reference number then you can use the measurements of your filter cartridge to find a replacement. When measuring your filter always take measurements of the length, diameter and any holes that appear on the top or bottom. It is also important to take note of any connections on the bottom of the filter as the replacement you buy will need to have the same connections.

Measure the length of the filter

Measure the diameter of the filter

Measure the diameter of any holes at the bottom

Measure the diameter of any holes on the top





Hot Tub Manufacturer

Finally if the two previous methods don’t work you can also find your replacement filter by searching for filters suitable for your hot tub manufacturer. However as mentioned earlier in some instances there are several filters available for the same manufacturer so try and have either a reference number or measurements available as well.

We have a wide range of replacement filter cartridges available to buy on our website

Algae in the corners of a tiled pool


If you have algae growing in the corners of your tiled pool it can often be difficult to remove by just doing a normal shock dose. This is because the circulation of the water often doesn’t reach those areas and hence chlorine doesn’t either. Any chlorine that you add will kill any micro organisms and algae in the main body of the pool but it may not kill any algae in difficult to reach areas such as the corners of the pool. If left untreated the algae can multiply rapidly and you could soon be faced with a pool that is completely green.

To kill any algae in the corners of your pool it is recommended that you shock the pool with calcium hypochlorite (500 grams per 10,000 gallons) as normal. However in addition to this put some gloves on and sprinkle some calcium hypochlorite granules directly into the corners where the algae is situated. Using an algae brush, brush the granules over the algae. The combination of physical cleaning and the very high local concentration of chlorine should kill the algae and remove it from the corners. When you have got rid of the algae add 1 litre of polyquat algaecide and then 100 millilitres per week to prevent recurrence.

Foaming in Spas and Hot Tubs


One of the most common problems spa and hot tub owners get is a layer of foam on the surface of the water. This is caused by a reaction that takes place between the natural alkalinity of the water and the bathers body oils. If the bather hasn’t showered before getting in the water then any cosmetic products, suntan lotions or detergents will wash off into the water. Obviously this can be prevented by showering before getting into the water, however this is not always possible. With this in mind you may need to add Antifoam to get rid of any excess detergents. Antifoam is an inert silicone based product used to effectively control foaming in hot tubs and spas. Adding approximately 50ml directly to the spa or hot tub should solve the problem.

Another cause of foaming is soft water. If you have a low calcium hardness level then this needs to be increased to at least 200 ppm to prevent foaming.

Maintaining a Hot Tub in a Hard Water Area


If you take a look inside your kettle do you see a build up of scale? If you do then the chances are you live in a hard water area. If you have a hot tub and you live in a hard water area then there are various things that you need to be aware of that will affect the running of your hot tub.

Hard water occurs due to the rain water filtering through soluble rock such as limestone and chalk, resulting in mineral salts like calcium dissolving into it. In terms of your hot tub water this usually means that you will have a high calcium level, high pH level and high alkalinity level. High levels of calcium are not good for your spa. Not only can calcium deposits (scale) appear on the surface of your spa, but scale can also build up on internal pipe work and heater, just like it does on the inside of your kettle. This can lead to substantial damage if not treated accordingly with a scale inhibitor.

The main chemical that makes water hard is calcium bicarbonate. The calcium part is the hardness whilst the bicarbonate is the alkalinity. As a result you will probably also have a high pH level and high alkalinity level. Both of these issues can be rectified by adding a pH Reducer, which is usually sodium bisulphate.

There are a couple of additional things you can do to help if you do live in a hard water area. From a chemical perspective it may be prudent to run your hot tub on bromine as you can maintain a pH level between 7.2 and 8.2. If you run on chlorine then you must keep the pH level between 7.2-7.6 so it is more difficult to sustain a suitable pH level.

Finally you can try and remove calcium from your water supply when you refill your hot tub by using the Darlly Pure-Stream Pre-Filter. This is an ion exchange resin pre-filter which attaches to your hose pipe and removes unwanted calcium and magnesium from your incoming water supply and replaces it with soft sodium instead.

Sea lion takes a dip in public swimming pool


This article caught our eye in the Daily Mail on Monday. Swimmers at an open-air public swimming pool in Dunedin, New Zealand were given a surprise recently when an unexpected guest turned up. At around 2.30pm holidaymakers and locals were joined in the pool by a sea lion who had casually made its way past reception and cafe before taking the plunge into the saltwater pool. Although New Zealand sea lions are known not to fear humans, swimmers quickly evacuated the pool and after a nice leisurely swim, the sea lion made its way out of the pool and back to its normal surroundings.

Hot Tub Starter Kits


Happy New Year to you all!

If you are thinking of purchasing a hot tub, shortly after installing it you will need to purchase some chemicals in order to keep the water safe to bathe in. If you are not experienced in maintaining a hot tub it can be daunting when faced with all the different chemicals. What are they? What do they do? How much do I need? These are probably just a few of the questions running through your mind. However, there is a simple answer to all these questions. Buy a chemical starter kit!!

Starter kits offer a cost effective and hassle-free method for ensuring you get your hot tub up and running and safe to bathe in. The basic starter kits on the market will contain chlorine (or bromine), a shock treatment, water balance chemicals and some test strips. These are the essential chemicals that you need to get your hot tub started. However, it is important to note that when maintaining a hot tub the likelihood is that you will need to use additional chemicals in the future, such as a water clarifier, filter cleaner, antifoam and perhaps a scale inhibitor if you live in a hard water area. It is therefore advisable to purchase a starter kit that also contains these additional chemicals. It may be more expensive at the start but you will save money in the future. Also if you do encounter any problems, such as foaming, you will have the peace of mind of knowing that a short trip to the garage or shed will sort the problem out quickly.

All good starter kits should also come with an instruction leaflet on how to run a hot tub. These are often quite extensive and provide a great deal of valuable information. This will help to ensure that maintaining your hot tub is a hassle-free experience.

We have a range of hot tub starter kits on our website, all of which include clear instructions on starting and maintaining your hot tub. Please click here for more information. If you are unsure on whether to use chlorine or bromine then please read our relevant blog post on this subject.

Chlorine or Bromine in a Hot Tub?


One of the most common questions we get asked from spa and hot tub owners is which is the best sanitiser to use – Chlorine or Bromine? There are many theories out there as to which is better, however we decided to gain firsthand experience and run our test hot tub on both in order to provide you with a practical answer. The conclusion we came to is that both are perfectly suitable sanitisers, however bromine does boast three crucial advantages over chlorine, which we believe makes it a more suitable sanitiser for hot tubs.

Less odorous – Running your spa on chlorine can create a strong chlorine smell in the water even when the chlorine level is kept within the recommended range of 2-4 ppm. Although this is perfectly normal it can result in an unpleasant bathing experience. Bromine is less odorous than chlorine and as a result this smell doesn’t exist and a more pleasant bathing environment can be enjoyed.

Effective at a broader pH range – The recommended pH level for a chlorine spa is 7.2 – 7.6. This is because the effectiveness of the chlorine as a sanitiser significantly decreases at higher pH levels. Bromine on the other hand, is an active santiser at pH levels of 8.2, therefore the pH level can be maintained at a much broader range of 7.2-8.2. This allows more flexibility when controlling the pH level and is particularly beneficial for hard water areas where the incoming water supply naturally contains high pH and alkalinity levels.

Slower dissolving – Regardless of which sanitiser you use, both are available in tablet form and ideally should be used in conjunction with a floating dispenser. The main difference we experienced is that bromine is much slower dissolving than chlorine and as a result it is a lot easier to maintain the correct sanitiser level in the water. This is crucial in order to reduce the amount of work involved in maintaining your hot tub.

To make this a fair argument it is only right that we look into the disadvantages of using bromine over chlorine. As bromine is slow dissolving it can have difficulty in recovering an adequate concentration after the hot tub has been heavily used or is started up after being emptied. In this case you need to add another sanitiser such as oxy shock or stabilised chlorine granules just to boost the level. Another disadvantage is price, as bromine is a little more expensive than chlorine.

Despite these drawbacks we firmly believe that the advantages of using bromine over chlorine far outweigh the disadvantages. As a result we would always recommend using bromine as opposed to chlorine in a hot tub.

Emptying a spa or hot tub


Even though your spa water is continuously re-circulated, treated and filtered, not all the pollution added by bathers to the spa will be removed. With this in mind it is important to drain and refill your spa on a regular basis. There are no set rules as to when you should do this however it is recommended that the water be changed after 100 bathers per 1000 litres of spa water. For example a 1500 litre spa would need to be drained after 150 bathers. If there are 2 bathers a day then it would need to be changed after 75 days.

Regardless of how many bathers use the spa the water should be changed at least every 3 months. This is a good opportunity to give the spa a good clean before starting the start-up procedure again! Before you empty the spa we recommend adding some spa and hot tub pipe cleaner to the water. Add 250ml per 1000 litres of spa water, directly to your spa and run the jets for one hour. Drain and rinse the spa thoroughly.

Closing your pool for winter


Now we have entered September pool owners will start thinking about closing their swimming pool down for the winter. This procedure is very important for two reasons. Firstly it helps ensure your pool is in the best condition possible when you come to open it up again in the spring and secondly it helps protect your pool and its fittings from the winter conditions. You can close your pool down by following the simple steps below.

  1. Backwash the filter and clean the strainer.
  2. Check the pH is between 7.2 and 7.6 and use sodium bisulphate (to lower pH) and sodium carbonate (to increase the pH) to adjust if necessary.
  3. Using Chlorine Shock (calcium hypochlorite), boost the chlorine level to remove any algae that maybe present in the pool. The recommended dosing rate is 1kg per 10,000 gallons of pool water.
  4. To prevent algae from growing add Winterising Algaecide. The recommended dosing rate is 2.5 litres per 10,000 gallons of pool water.
  5. Turn on the circulation to disperse the solution through the water for a period of 24 hours.
  6. Reduce the water level to just below the skimmers. This is to allow for any extra water that enters the pool, ie rainfall, therefore preventing it from overflowing. WARNING: Do not lower the level too much especially if the water table is high as this could cause structural damage to the pool shell.
  7. To protect any exposed metal surfaces, drain the water from the pump(s), filter(s), heater and pipework.
  8. Leave any valves above the water level open. Any below should be closed to protect from frost damage.
  9. Switch off the electricity supply to the system.
  10. Cover the pool with a heavy-duty winter pool cover.
  11. Check the appearance of the water, and the chlorine/pH levels occasionally during the winter.

By following this set of guidelines it should significantly reduce the amount of work you have to do when opening the pool up in the spring. Winterising Kits are available from our website which include all the chemicals you need as well as step-by-step instructions.

Please note the information provided on this page is believed to be correct but is given without warranty and no liability is accepted or implied. Please use this information in conjunction with manufacturers instructions.

Removing chlorine from a pool


Dechlorinator is a sodium thiosulphate solution that allows you to safely remove chlorine from your pool should accidental over-chlorination occur. It isn’t recommended to swim in water that contains more than 3ppm of chlorine however you shouldn’t use Dechlorinator unless the chlorine level goes above 10ppm. If your chlorine level is between 3 and 10ppm it is recommended that you stop dosing your pool with chlorine and allow the chlorine level to come down naturally over time. The reason for this is if you put too much dechlorinator into the pool then you will need to add a lot of chlorine to establish a chlorine level again. This is good for chemical suppliers profits but not for your pockets!!!

Before you add any dechlorinator it is important that you ascertain an accurate chlorine reading. This may involve doing a dilution test if the chlorine is bleaching out your test reagent. Once you have an accurate chlorine reading, pour the required amount of dechlorinator into a bucket of water and then distribute evenly around the pool. Allow the pool water to turnover twice before testing the pool water again.