Galvanic Corrosion
Galvanic Corrosion is the process where dissimilar metals are submerged in an electrolyte solution (salt water). When submerged these differing metals will develop a tiny potential voltage between them. This is the exact same process that a battery uses and is also a very common problem with salt water pools.
When you think about it a swimming pool is filled with electrolytic solution - salt water. Inside the pool and part of the pool equipment are all sorts of metals such as nickel, galvanized steel, copper and titanium. Since all of these metals are located in the salt water it is possible to develop a small electric charge across these different metals.
Does Salt Water Damage Pools?
Over time this very small voltage would cause severe corrosion of whichever metal is the weaker of the two. Titanium and stainless steel are more resistant where copper and galvanized nickel steel and zinc are much more inclined to corrode. It is very possible to develop severe damage to structural components of the pool in this way including galvanize steel walls of vinyl liner pools and re-bar steel from concrete pools. You can also corrode pool equipment such as heaters at an extremely accelerated rate.
If the pool is not properly bonded this can make the galvanic corrosion much worse. Even if the pool is bonded often the corrosion severs the copper bonding wire which sees the pool take a turn for the worse very quickly. There is some good news however as there is a process to help prevent this from happening, but unforunately almost no salt water pool owners have one.
Sacrificial Annodes & Salt Water
A sacrificial zinc electrode or series of zinc plates are added to the system so that they become the weak link in the chain. Zinc will corrode faster and more readily than any other metals so as long as you keep the system in fresh supply of zinc plates to corrode then all the other metal components should last. Be sure to understand the process of galvanic corrosion before you install a saltwater system to prevent damage to your backyard investment.
Chlorine VS Salt Water Pools
One of the biggest problems that pool owners can encounter in a pool with a salt water system is a lack of chlorine available in the water. The generator cell creates chlorine slowly over a period of time and there are some cases where the chlorine will dissipate or be used up as fast or faster than it is produced.
It is for this reason that salt water generator systems for swimming pools are regarded as maintenance chlorination systems. It is normal for the function and operation of salt water systems to need to manually adjust the chlorine levels periodically.
Salt Water Pool pH
A final note on the limitations of salt water systems, perhaps less of a limitation and more of a common situation that pool owners with salt systems will encounter, is an upwards pH creep.
The type of chlorine that salt water systems generate has a high level of pH. While there are other forms of chlorine with high pH that can also cause this problem, it tends to be more noticeable in pools with salt water systems.
Controling pH With Salt Water Pools
Some chlorine products have a low pH and one form of chlorine has a relatively neutral pH. The chlorine produced as a result of electrolysis has a pH nearing that of 13-14 which is on the extreme end of the alkalinity spectrum.
This causes your pH to creep upwards quite easily. If the total alkalinity in the water is too low this would allow your pH to swing upwards wildly as there is little buffer in place to prevent it from fluctuating. A strong understanding of total alkalinity and overall swimming pool chemical balancing is required if you want to be able to balance your salt water pool.
Is Salt Water Bad For The Pool?
The limited scope of this website could not begin to explain the electrical theory behind the nature of this question. Most pool builders and installers would not be able to tell you what galvanic corrosion is however this is a very real concern for salt water pool owners. Galvanic corrosion is the result of transient electrical currents in the pool water.
In simple terms the swimming pool is acting like a battery. It is filled with a saline solution and has contact with different types of metals - just like a battery does. The end result sees a small potential voltage that can cause failure of the weakest metals in the system unless a zinc plate designed to act as a controlled failure is added to the plumbing system.
So you want a salt system for your pool so you need to know how to convert to a salt water pool