What’s going on under that cover?
Not too much you hope.
For clean, clear, water you need three things.
Circulation, filtration, water chemistry management including some kind of sanitizer.
It’s a good idea to test that water again before you go inside for the winter.
If your swimming pool finish is damaged it won’t be an easy fix.
What could happen?
I’ve seen these two problems over and over.
On a vinyl liner swimming pool this error won’t just fade away.
The pool owner uses chlorine pucks as the in season sanitizer.
This chemical has a low pH causing the water to become very acid quickly.
Low pool use, cooler weather and the usual dose of chemicals have caused a concentration.
The pH and alkalinity are low and the chlorine is high.
The water is below 7.0 and now acidic.
The person closing the pool picks up one of those one size fits all closing kits.
The tired old test kit could work but the chlorine is so high it bleaches out the test.
It must be too old. It’ll be alright.
So in goes all of the closing kit, algaecide, metal magnet, and more chlorine.
Chlorine is slow at a high pH it does not work well.
Chlorine is super active at a low pH.
In this case you will have a stiffer, lighter shade of liner by spring.
It will bleach out the liner and take away the elasticity.
On a plaster swimming pool the situation above will cause chalking.
In my area of the country we have soft water.
To keep the finish on your plaster pool smooth, water chemistry is the most important thing.
You can ruin a brand new plaster job in a few weeks.
It takes plaster some time to cure, as long as 18 months.
Until it cures it has not hardened fully.
So, fresh plaster is easier to damage. Great huh?
Around here we need to make the pool water harder.
The water will try to pull the minerals it desires from that plaster.
It wants calcium.
Unchecked under a cover the plaster will be ruined.
The walls and floor will begin to feel like sandpaper and dust (chalking) will waft away from every place you touch.
You won’t brush this away, brushing will now make a cloudy mess.
An ounce of prevention.