Yes. All large pools need to be treated to keep dangerous bacteria from forming.
You have to treat pool water with pool chemicals and use a pool filter to get and keep the water clear.
You do not treat pool water hardness with chemicals. If you have hard water in your area then you need to know what the allowable maximum of water hardness is before the water needs to be changed. You remove or reduce the hardness in water by draining and refilling the pool. K
You should first get a lab test on the water. It may be perfectly good for pool use - but you won't know without a lab test.You should first get a lab test on the water. It may be perfectly good for pool use - but you won't know without a lab test.
The amount of chlorine that is needed to treat a pool on a weekly basis will depend greatly on the size of the pool. A person should consult with a pool specialist before dosing their home pool.
If you are not worried about the pool floating on a high water table or you have a hydrostatic valve on the bottom. I would drain it clean it and start again.
Chlorine is an effective agent against treating your pool against bacteria. You can buy supplies to test and treat your pool at pool shops.
Drain it and refill it
you should use a chlorine floater, shock it once a week and add algaecide weekly as a preventative.
No, water should not be kept in your pool all winter. When it gets cold enough, the water will freeze. When water freezes, it expands. So when the water in your pool freezes and expands your pool will be ruined.
on the side going into middle of pool
They may have treated areas around the pool, but don't treat the water itself. the only water treatments done routinely are in stagnant water for mosquito larvae.
You can, if the water presently in the pool is 'hard' - but be very careful to keep an eye on the Calcium Hardness of the pool water. If you filled a pool with water from the softener, the water would be hungry for calcium and drag it out of the pool walls, making them feel and look like sandpaper. Calcium hardness should be kept within 200-275ppm. best to use regular water for topup and keep the pool water properly balanced (see your local pool store).