A salt water pool filter uses a generator to create chlorine through electrolysis. Chlorine gas is released from the salt (sodium chloride instead of calcium chloride) and combined with the water. In this way, chlorine is still present only in a more natural state, which is less harsh on the skin and hair. The chemical balance of this process is important to keeping filters running optimally.
Over Active Generator
A generator keeps chlorine levels regulated in the pool by activating and adding chlorine when necessary. The generator is the expensive part and, when overused, tends to wear out quite quickly. When the stabilizer levels and pH levels are regulated, the generator only has a minimum of work to do to keep chlorine levels balanced. However, if the chemicals in the pool are not monitored frequently and the generator is over working it can easily break.
The pH levels within the pool need to be between 7.4 and 7.6 in order for the chlorine to be effective. High or low pH can result in false negative readings and over chlorination causing corrosion of the ladder, pool fixtures, lining, or the generator itself.
High phosphates cause algae to begin growing. Long before the algae becomes visible, the pool filter will overextend trying to kill the algae, causing low salt levels and an over active generator. Commercial stain removers for pools and runoff from lawn fertilizer are extremely high in phosphates, so be careful when either are applied in or around the pool.
Too Little Salt or Too Much Salt
The filter light indicates when salt needs to be added to the pool and often won't turn on when the salt balance is dramatically too high or too low. Before any salt is added to the pool, manually check the water to insure over-salting doesn't occur. Secondly, low salt levels (less than 2000 ppm) can cause destructive oxidation levels of the anode within the generator. If the salt levels are too high or too low it can indicate that the generator is starting to go out and thus not regulating the salt content well.
Stabilizers (Cyanuric Acid) neutralize the effects of sunlight and heat on the chlorine in the pool. Since sodium hydrochloride is being turned into chlorinated gas and then bonded to water, heating can evaporate the chlorinated gas. By adding a stabilizer, these bonds are fortified. When stabilizer levels are low, the generator has to compensate for the loss in chlorine, over working the system. 80 parts per million is recommended by most manufacturers, but in some humid or especially sunny places 120 parts per million is needed. Check with your manufacturer or pool supply store for recommendations on stabilizer levels.
Calcium Build Up
If large amounts of calcium are present in your water, salt water pool filters generally magnify this issue causing build up. Clean the filter's generator frequently or it can freeze up completely.