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One way to find a leak in a pool liner of an above ground pool is by using food coloring. When you add the food coloring in small amounts, you can see it leaving the pool through the leak.
google above ground pool repair
Do a goggle search find above ground pool repair k
look for the wet spots. where the grass is greener is usaully a clue. fittings that night be leaking or hole in liner.
Put a small amount of food coloring in the area of the pool you think is leaking and watch the food coloring disappear in the hole
you will find that people will swear by either method and then others will say in ground gunite or concrete is best . If properly maintained they are all much of a muchness. from what I have seen When they are new the vinyl pool looks better. the problem is that the vinyl will need to be replaced eventualy while you wont have this problem with fiberglass.
They don't make them for in ground.
My advice is to contact the manufacturer of the liner and get their advice. at least find out what type of glue works on the liner and if you can get a piece of it to cover the tear. I have always found that when you ask nicely company's can be very helpful.
you can find lodestone above ground, but not below ground.
Put your winter plugs in blocking off all flow to the pipes and etc. If the water still drops, it's in your pool.
You mean a cover like to close the pool over top of the water or a liner to hold the water. To cover over the water, some companies make vinyl covers, they tend to be more expensive and heavier then woven ones though. As far as a liner, some manufacturers choose not to make Vinyl Liners for concrete pools for different reasons. You'll have to check with a dealer in your area to find a supplier that does, or pursue other repair options.
Vinyl liner patch kit are available at pool dealers and at stores like Walmart. They usually consist of some clear vinyl and some liquid glue. The best thing is to use vinyl that matches your pool liner. I always save scraps when new liner is installed. First trim the patch to cover the hole. A round or oval patch works best since there are no corners to peel off. Next clean the place to be patched. Then cover the back of the patch with glue. If the tear is under water fold the patch together with the glue on the inside. Next open the patch and place it over the tear and press the air out starting from the center working outward. If the tear is deep under water you may need to find a diver.