What is exactly the same
People sometimes picture a salt water pool as a different kind of structure. It is not. The hole in the ground, the shell, the plumbing and the filtration are identical to a traditional chlorine pool.
That holds for all three common construction types:
- Concrete
- Gunite or shotcrete sprayed over a steel frame, then finished in plaster, pebble or tile. The most flexible in shape and size.
- Fiberglass
- A factory-made shell lowered into the excavation. Quick to install, in a fixed range of shapes.
- Vinyl liner
- Wall panels and a fitted liner over a prepared base. The lowest starting cost of the three.
Any of them can be a salt water pool. The pump draws water out, the filter cleans it, the heater warms it, and it goes back in. Salt changes none of that.
What is different
The difference is how the water is sanitized, and that has four knock-on effects for the build.
| Part of the build | Traditional chlorine pool | Salt water pool |
|---|---|---|
| Sanitizing equipment | A feeder, or chlorine added by hand | A salt chlorine generator on the return line |
| Heater | Standard copper heat exchanger is common | Cupronickel or titanium heat exchanger |
| Metal fittings | Fewer restrictions | Marine-grade stainless or composite |
| Bonding | Required by code | Required by code, and more consequential |
| Stone and coping | Most stone is suitable | Dense or sealed stone |
The salt chlorine generator
This is the one component a chlorine pool does not have. A salt chlorine generator has a control unit and a cell. Pool-grade salt, which is nearly pure sodium chloride, is dissolved in the water, and as that water passes through the cell, electrolysis converts some of it into chlorine.
Position matters. The cell is plumbed into the return line after the pump, the filter and the heater, so it is the last thing the water passes before going back to the pool. Chlorine is at its strongest right as it leaves the cell, and you do not want that running through a heater.
The chemistry is explained in how salt water pools work.
Salt-compatible equipment and metals
Salt water at pool strength is mild, roughly a tenth as salty as the sea. It is still more corrosive than fresh water, and it finds the weakest metal in the system.
- The cell. Plates are titanium with a specialist coating, made for the job.
- The heater. Choose a heat exchanger in cupronickel or titanium. Plain copper wears faster in salt water.
- Lights, rails and ladders. Marine-grade stainless steel or composite. Ordinary stainless can pit and stain.
- Fittings and fixings. Avoid unprotected brass, copper and plain steel anywhere the water reaches.
- Automatic covers. Some track and mechanism parts are rated for salt and some are not. Check before specifying.
Bonding and grounding
Every pool has to be bonded. Bonding connects the metal parts of the pool and its surroundings, such as the steel in the shell, rails, light housings, pump motors and the heater, with a continuous copper conductor so that they all sit at the same electrical potential.
In a salt water pool this deserves extra care. Salt water conducts electricity better than fresh water. If one metal component is left out of the bonding grid, small stray currents can flow through the water and accelerate corrosion on that part.
This is electrical work governed by code and inspected by the local authority. It should be done by a licensed electrician who builds pools regularly, and it is far easier to get right during construction than to correct afterwards.
Stone, coping and decking
The other place salt shows up is at the edge. Water splashes onto the coping, evaporates and leaves salt behind. Over many seasons that can pit or flake soft stone.
- Dense stone, porcelain and well-made concrete pavers cope well.
- Soft limestone and some sandstone need sealing, and resealing, or a different choice.
- Rinsing the deck with fresh water from time to time helps in dry climates where salt builds up.
It is a design decision, which is why it should be made before the pool is drawn. More on the trade-offs in benefits and drawbacks.
Does the construction type matter?
- If you want the fewest materials exposed to salt
- Fiberglass or vinyl liner.
- If you want a custom shape, a lagoon or a built-in hot tub
- Concrete, with salt-tolerant finishes.
- If the pool has a vinyl liner and steel wall panels
- Protect the panels and fix any liner leak quickly.
- If you are adding salt to an existing pool
- Check the heater, metals and stone first. See converting to salt water.
Why to decide before the build starts
Because the structure is the same, it is tempting to treat salt as something you can decide later. You can, but it costs more. The heater, the light fittings, the rails, the coping and the bonding details are all chosen and installed during construction.
Decide on salt at the design stage and every one of those is specified correctly the first time. That is how we approach every salt water pool we design.
