The best sand filter I have seen up to now is one that I scored along with a new magnapool chlorination system last year. I have never seen the water kept as clean as it is now. The trick is not so much in the filter as in the filter media. Instead of sand this unit has a material called diamond cleenhttp://www.poolrite.com.au/new-products.htm
NO You would need an awful lot of acid to do any harm there.
You can get swimming pool filter sand or a number of other filter media that can be used instead of sand from most pool shops. You can also get sand from under above ground pools from a builders supply or nursery.
Yes, above ground pools must be maintained regularly. The chemicals must be kept in balance, the filter emptied, and bugs and debris skimmed out daily. Sometimes the pool liner and filter sand may need replacing, as well.
Probably not going to be adequate.
If you are getting sand coming into the pool and have a sand filter you may have to replace worn laterals in the sand filter.
It should be on "FILTER"
no the salt will disolve....
Probably not going to be adequate.
Alum is a floculent and these are often used to settle excessive amounts of dirt to the bottom of pools the are available from pool shops. It sounds like you will need to replace the laterals in your sand filter first so that you don't have this problem in the future. Take care vacuum the settled dirt and flock to waste do not put it through the filter.
That is most commonly referred to as " washed sand " also float sand , or mortar sand ,it has no stone or stone chips that will damage or stain the liner.
Sand
Usually the top of the sand filter is above the water level of the pool, so all you have to do is unscrew the top and look in. However if the filter is below the pools water level you will have to cut of the water coming from and to the pool before you do. who added the sand? If you did - did you follow the manufacturer's instructions as to how much and what type of sand to use? Instructions tell you - - SPECIFICALLY - - how many pounds of # 20 silica sand to use.