How To Set Up A Saltwater Filter Bed For The Hikki Bohemen Wood Fired Hot Tub

Our Hikki Bohemen hot tubs are constructed from aluminium so can safely be used with salt.  Although better for the environment compared to chlorine and other hot tub additives, saltwater will harm vegetation if not treated properly first. One solution would be to dump the used saltwater directly into the waste water system (i.e. down a drain). However, this is not an ideal solution in terms of waste water management. The ideal, is to re-use or re-purpose the water. Whether pumped back into the hot tub or used for irrigation, the water should not be wasted. The separate inlet and outlet valves present on the Bohemen hot tub make setting up an irrigation a relatively simple prospect.

A relatively simple, long-term solution to process this saltwater would be to create a saltwater filter bed for your garden (provided you have the space). This will remove the salt and other impurities from the waste water which can then be allowed to drain away into the surrounding landscape (or it can be collected for subsequent use).

List of materials you will need:

∙Shovel or digging equipment

∙Perforated pipe or drainage tubing

∙Geotextile fabric or landscape fabric

∙Coarse gravel

∙Fine gravel

∙Fine sand

∙Activated charcoal (optional but preferable).

∙Native salt-tolerant plants (optional but preferable).

Instructions:

Select the location: Choose a suitable area in your garden for the filter bed. It should be close to your saltwater source and have proper drainage. Ideally, choose an area that is at least 5 feet lower in elevation as compared to the hot tub, so that it can be emptied under the power of gravity.

Excavate the area: Dig a trench in the chosen location. Volume-wise, it should be roughly equivalent to the amount of water your hot tub holds. The Bohemen holds approximately 600 litres of water so a trench roughly 2 metres long by 1 metre wide by 1 metre deep should suffice.

Lay the perforated pipe: Place a perforated pipe or drainage tubing along the bottom of the trench. This pipe will help collect and subsequently distribute the filtered water evenly. The pipe should “stick out” from the side of the filter bed should you want to collect the water once it has been filtered. Alternatively, skip this step if you would rather let the water drain away naturally without collecting it i.e. you are not planning to reuse it.

Cover the pipe with geotextile fabric: Lay a layer of geotextile fabric or landscape fabric over the perforated pipe. This fabric acts as a barrier to prevent fine particles from clogging the pipe.

Add a 20cm layer of widely available activated charcoal on top of the fabric. This will help remove many chemical impurities from the water, including salt. 

Add a 20cm layer of sand: This layer will filter the water by removing finer sediments and impurities.

Add a 20cm layer of finer gravel: This further filters the water and keeps the sand beneath it in place.

Fill the trench with a 20cm+ layer of coarse gravel. This layer acts as the initial filter, allowing water to flow while trapping larger debris. It also helps keep all subsequent layers in place and deters digging animals.

Plant salt-tolerant vegetation in and around the filter bed (optional): If desired, plant native salt-tolerant plants in the filter bed. These plants can help absorb excess water and further filter the saltwater. Consult local gardening resources for suitable options. You can even plant certain edible plants!

Connect your Bohemen hot tub to the filter bed: Use a hose to connect the waste water valve and position it above the filter bed, so it distributes the water evenly across the surface of the filter bed. You can use a shower head or another perforated pipe to help with even water distribution.

Allow for filtration: Let the saltwater flow through the filter bed. The layers of gravel, sand, cloth and charcoal will work together to filter out salt and other impurities, allowing cleaner water to seep through.

Collect filtered water: Place a collection container at the outlet end of the filter bed to collect the filtered water for irrigation or other purposes.

Regular maintenance of the filter bed, such as removing accumulated sediment and monitoring plant health, is important to ensure its optimal performance.

Hikki suggest changing the water weekly in your hot tub, if using saltwater.

Another convenient set up for filtering saltwater makes use of large multi gallon buckets. Using similar filter media to the saltwater bed described above, the water passes through a series of connected buckets and upon exiting the system, should be clean. The benefits of this type of system over the the "filter bed" type system is convenience and saving space. No excavations are necessary and the footprint is much smaller. Maintenance is also easier to carry out as everything is conveniently held in buckets. 

Again, unless using an electric pump, the containers will have to be placed progressively lower down in respect to each other, if the source of power is gravity.

List of materials you will need:

∙Shovel or digging equipment

∙Perforated pipe, drainage tubing. shower heads

∙Geotextile fabric or landscape fabric or ground cloth

∙Coarse gravel

∙Fine gravel

∙Fine sand

∙Activated charcoal (optional)

∙Large volume plastic buckets/containers

Instructions

Choose an appropriate area - It should be in fairly close proximity to your Hikki hot tub. If possible, it should be 5 foot lower in elevation as compared to your hot tub. To save space, the buckets can be placed on individual platforms to raise them the appropriate distance from the ground, from the hot tub and from each other.

Set up the buckets and fill each one with the appropriate medium, trying to minimise air gaps. Connect the buckets in the sequence outlined in the below blueprint, with the final bucket being allowed to drain away to ground or large enough to hold all the water from your hot tub.

Finally, connect the Hikki output valve to the first bucket in the sequence (the one containing coarse and fine gravel), using a hose. 

Allow the water to filter through the system. This may take a couple of hours or longer, depending on the density of media used, elevation of buckets and of hot tub, pipe flow rates and other factors.

NB Please note - this is not an exhaustive plan. Given that these systems are "home made", they will probably require modification, improvement and maintenance. In other words, the appropriate system will need to be "tweaked" to get the best performance, for the relevant hot tub set up.

Finally, failing these solutions, there are "off the shelf" solutions available but these are definitely less planet and wallet friendly as they involve the use of electricity and chemicals. 

Good luck.

The Bushgear Team