Hot Tub Waterline Advice

Why ?

Waterline scum lines appear as a result of many different issues which can be summarised with an overall lack of user control of the maintenance of the hot tub.

Regular cleaning & balancing of the hot tub shell and spa water would reduce the chance of a build up to nil & keep the hot tub clean & clear.

Here below we explain how the scum lines appear and how to make sure your hot tub is stain free.


Ensure your chemicals dissolve properly into the water, as incorrect control will again result in a waterline of white.

This is the case in hard water areas where the chemicals take time to dissolve and also when using slow dissolving sanitisers such as Bromine.

A good tip is to pre-dissolve chemicals in a container of water and then apply to spa water after all is dissolved.



Maintain PH Levels

Managing your pool's water chemistry is a delicate balancing act.

The PH level range is recommended to be 7.2-7.6. 

High PH is a common cause of calcium and scale build-up which will show on the waterline whilst a low PH level will corrode metal parts and use allot of sanitiser which can lead to over dosing of the spa & then again lead to chemical staining.

To reduce this risk, balance the water on a regular basis and use PH plus or PH minus when appropriate.

Chemical Balance

Over dosing the hot tub with chemicals will lead to chemical staining of the waterline.

The fault lies with applying chemicals without first testing the water balance with testing strips

Keep your bromine / chlorine levels stable & correct to reduce the risk of staining

Shower Before Use

Before entering the hot tub, it is essential all users shower so all creams, oils, make up etc are removed.

Scum lines do appear on the waterline as the skin expels these partials back into the water which then build up around the water’s edge.

A shower will reduce the risk of this & with a weekly clean of the hot tub, the waterline should stay clean & free of scum.

Know Your Water

Water quality differs from area to area so a process which works in one City will differ from another.

Get to know your water and the understand there is a different procedure for hard or soft water.



What The Experts Say...

Waterline staining is a manifestation of lime scale, which is primarily deposition of calcium carbonate with other contaminates (usually dissolved metals such as iron and magnesium).  Scale occurs in a variety of aqueous containment systems like water treatment tanks, boiler tanks, aquariums and piping.  The phenomenon can occur on any surface such as metal, ceramic, glass or in the case of spas, acrylic.  When this occurs, it is due to loss of control of the chemical balance in the water.  It has nothing to do with the physical or chemical properties of the acrylic.  Maintaining proper control of the system chemistry is vital because scale is difficult to remove.  Depending on the composition of the scale, it can be quite resistant to descaling agents, many of which can chemically attack the acrylic, compounding the problem.  Often as not, the scale has to be removed mechanically with abrasives followed by polishing.  It is far preferable to avoid the deposition of scale rather than mitigating the result after it occurs.  

Justus Medley




What The Experts Say ...

Spa manufactures provide detailed guidance for balancing the chemistry of the of the spa water.  Upon the first signs of scaling, it is far preferable to drain the system and start anew than to try and rebalance the chemical mix.  It is a natural temptation to overdose the system with chemicals.  We strongly recommend that you resist that temptation because it is an ineffective strategy that will only aggravate the deposition of scale.  Remember that the system is constantly losing water and concentrating the mineral/salt content of the spa water.  Addition of make-up water does not dilute it back to the previous concentration.  No initial fill can be maintained indefinitely without scaling eventually starting.  If the source water is high in minerals, metals, and salts (hard water) this will drastically reduce the amount of time that the system can be maintained.  A water softening system is essential when the source water is over a certain hardness.  It is of course preferable to use a softening system no matter how soft the source water may be.  Aggravating factors like lotions, perfumes, soaps etc should be prevented by showering before entering the spa.

Justus Medley








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