Discoloration, Deterioration and "Dry Rot" Above the Water Line
In most cases, these three problems are different stages of the same phenomenon. The cause of these problems are many and varied, but have a universal theme.
In most cases, the discoloration (usually brown), the deterioration (stiffening of the vinyl) and then the complete failure of the vinyl, commonly referred to as "dry rotting", is due to the extraction of the plasticizers and stabilizers from the vinyl.
(Plasticizer is the additive which gives the vinyl its flexibility, stabilizers give the vinyl its high temperature stability.) Under normal circumstances, the volatility of these additives is very low and the vinyl will maintain its physical characteristics for many years.
Experience has taught us that under certain circumstances the area above the water line can begin to deteriorate very quickly. There are three main contributors to this problem; chemical attack, high temperatures and UV rays. The UV resistant characteristics of pool vinyl is excellent and by itself the UV rays do not present a significant problem. However, acid based vinyl cleaners, when not rinsed completely from the vinyl, exposed to extremely high temperatures and the effects of UV rays, will accelerate deterioration of the vinyl liner. There are however, certain steps that can be taken to combat these problems.
We had found, through laboratory testing, that acid based vinyl cleaners will adversely affect the life of the vinyl. Exposure to sun light and high temperatures will greatly accelerate that deterioration process. From a vinyl standpoint, we do not recommend using any cleaners that contain acid. If you do use an acid based cleaner, you must rinse all traces of the cleaner from the vinyl. If you do not remove all traces of the cleaner, you are creating a situation where accelerated breakdown of plasticizer and stabilizer will take place, thereby significantly shortening the life of the liner. Use alkaline based cleaners. They are more vinyl friendly and they work just as well as the acid based cleaners. In all instances, rinse the liner fully.
Clean your pool often by taking a soft cloth and using the pool water to rinse contaminates from the vinyl. Substances such as body oil, sun tan lotion, baby oil, etc., will collect at the line. These substances, when exposed to the sun and the high temperature that can be found just above the water line, will often times turn brown and be very difficult to remove from the vinyl.
If it is an option, have at least a two foot radius, or larger, corners in your pool. This will lessen the stress put on the vinyl in the corners. Insist that the liner fit properly. Watch the installation of the liner. If it has to be "stretched in", insist on a looser fitting liner. If the liner is too small it will tend to pull away from the wall above the waterline and especially in the corners. On the sun side of the pool, temperatures can reach in excess of 180 degrees Fahrenheit, between the liner and the sidewalls. These areas that pull away are the areas that generate the highest temperatures and are the places that will fail first. Remember: Stressed vinyl is more susceptible to chemical and environmental attack.
With proper cleaning and a properly fitted liner, there is no reason why your liner should not last many years. However, unless you follow these simple rules, your liner's life will be significantly shortened.