The current rave is have a "salt water" pool. Many owners are under the false impression that these pools are "chlorine free." Though, this is hardly the case.
Electrolytic Solution
Salt is placed into the pool to create a solution much weaker than that found in the ocean. In fact there should only be about 3,000 ppm of salt present in a salt water pool. A special device at the equipment pad, then splits the sodium chloride (salt) into CHLORINE! These owners are merely using the salt to generate chlorine in their pipes!
But placing salt into the pool also turns the pool water into a electrolytic solution. Add some stray current and the pool becomes in effect a giant electroplating tank.
A salt water pool is really a very weak, but giant battery!
Galvanic Corrosion
These stray currents will cause staining of the plaster surfaces, galvanic corrosion of less noble metals. Copper heat exchangers will actually dissolve from the inside and decay on the outside, as their molecular structure is attacked. Metals suspended in the pool water will bond to more noble metals, plating them in unusual colors.
Sacrificial Anode
Many in the pool industry have drawn on "a solution" that boat owners have used for years - SACRIFICIAL ANODES. HOWEVER, a SACRIFICIAL ANODE is not the placebo everyone is seeking.
On a boat, a sailor does not care if the anode erodes, or if the anode's metals dissolve into the water (ocean). The anode on a boat is a lot cheaper than the wiring, an expensive bronze prop or brass components. It prevents the corrosion of the boat's precious components, by SACRIFICING itself instead.
Placing a sacrificial anode in a swimming pool is doing the same thing as on a boat. One is merely offering a SACRIFICIAL metal for the galvanic corrosion to attack, instead of the precious components. It does nothing to address the actual cause - GALVANIC CORROSION.
So instead of plating surfaces with copper, you will be plating them with zinc or magnesium from the sacrificial anode. The sacrificial anode will save the copper, but it will not stop the staining or plating of the stainless steel components. That will now occur with the metal from the anode.
This is exactly why anodes need to be periodically replaced - they are sacrificed. And where those sacrificed metals go is out of your control!
The Source of Stray Current
The equipotential bonding grid does not prevent galvanic corrosion. In fact, if there is stray voltage finding it's way to the pool through the property's CONTINUOUS GROUNDING SYSTEM, the equipotential bonding grid may actually be feeding voltage to the pool's metallic components.
The bonding grid can actually function as either the electrode or cathode, depending if there is stray voltage present or if it is providing a path to ground (where the equipotential bonding grid and the grounding grids are cross connected - pumps, heater's, panel boards, etc).
For these very reasons, many pool builders that I know and I, have ceased installing salt systems. We now promote "off-line" on-site generation of liquid chlorine from salt or tanks of liquid chlorine and then the controlled dispensing via a ORP/pH Controller.
Paolo Benedetti, SWD Aquatic Artist, Watershape Consultant, Expert Witness, International Construction Management
Contact the author at: info@aquatictechnology.com or 408-776-8220
"Creating water as art."™
Aquatic Technology Pool and Spa©
©www.aquatictechnology.com
All rights reserved.
Electrolytic Solution
Salt is placed into the pool to create a solution much weaker than that found in the ocean. In fact there should only be about 3,000 ppm of salt present in a salt water pool. A special device at the equipment pad, then splits the sodium chloride (salt) into CHLORINE! These owners are merely using the salt to generate chlorine in their pipes!
But placing salt into the pool also turns the pool water into a electrolytic solution. Add some stray current and the pool becomes in effect a giant electroplating tank.
A salt water pool is really a very weak, but giant battery!
Galvanic Corrosion
These stray currents will cause staining of the plaster surfaces, galvanic corrosion of less noble metals. Copper heat exchangers will actually dissolve from the inside and decay on the outside, as their molecular structure is attacked. Metals suspended in the pool water will bond to more noble metals, plating them in unusual colors.
Sacrificial Anode
Many in the pool industry have drawn on "a solution" that boat owners have used for years - SACRIFICIAL ANODES. HOWEVER, a SACRIFICIAL ANODE is not the placebo everyone is seeking.
On a boat, a sailor does not care if the anode erodes, or if the anode's metals dissolve into the water (ocean). The anode on a boat is a lot cheaper than the wiring, an expensive bronze prop or brass components. It prevents the corrosion of the boat's precious components, by SACRIFICING itself instead.
Placing a sacrificial anode in a swimming pool is doing the same thing as on a boat. One is merely offering a SACRIFICIAL metal for the galvanic corrosion to attack, instead of the precious components. It does nothing to address the actual cause - GALVANIC CORROSION.
So instead of plating surfaces with copper, you will be plating them with zinc or magnesium from the sacrificial anode. The sacrificial anode will save the copper, but it will not stop the staining or plating of the stainless steel components. That will now occur with the metal from the anode.
This is exactly why anodes need to be periodically replaced - they are sacrificed. And where those sacrificed metals go is out of your control!
The Source of Stray Current
The equipotential bonding grid does not prevent galvanic corrosion. In fact, if there is stray voltage finding it's way to the pool through the property's CONTINUOUS GROUNDING SYSTEM, the equipotential bonding grid may actually be feeding voltage to the pool's metallic components.
The bonding grid can actually function as either the electrode or cathode, depending if there is stray voltage present or if it is providing a path to ground (where the equipotential bonding grid and the grounding grids are cross connected - pumps, heater's, panel boards, etc).
For these very reasons, many pool builders that I know and I, have ceased installing salt systems. We now promote "off-line" on-site generation of liquid chlorine from salt or tanks of liquid chlorine and then the controlled dispensing via a ORP/pH Controller.
Paolo Benedetti, SWD Aquatic Artist, Watershape Consultant, Expert Witness, International Construction Management
Contact the author at: info@aquatictechnology.com or 408-776-8220
"Creating water as art."™
Aquatic Technology Pool and Spa©
©www.aquatictechnology.com
All rights reserved.
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If you want to ask a question of Paolo Benedetti, you may email him at: info@aquatictechnology.com