One reason that causes sand to accumulate at the bottom of your pool is a sand filter with a broken lateral or laterals. Notice where the sand is accumulating? Is their return outlets from the filter directly above the small piles of sand in your pool? That is a broken lateral. You can fix this problem by scooping out the sand in the filter and replacing the laterals at the bottom of the tank. I have been cleaning and repairing pools for a long time and it is my suggestion that you hire a professional for this job.
no, it probably just means someone went in the pool with dirty feet.
Swimming pools can have many types of bottoms. Most are cement or dirt. So if its cement and bumpy its probably wearing and the same if its dirt. When the pool was put in on top of the dirt is sand usually so the sand has shifted. The water stays in because most pools have liners.
YES
sand
This sounds as thought the laterals in your sand filter are worn. Laterals are horizontal spokes at the bottom of your sand filter with tiny holes in them that let water through but not sand. After a time the holes get enlarged and start allowing sand through and back into the pool
Sand blasting is not the answer to a good prep for a replaster job
You can't, I have never heard of any one converting any type of pool. The pool has to be taken out and then you can rebuild a new pool or fill in and put new pool in a new spot cost wise it is not feasable.
The sand should last for a long time in some cases years. If you see sand in your pool in probably means it is time to change or if the pool looks cloudy that could mean sand is soft (has lost sharp edges). if you take some in your hands and rub them together it should feel very coarse if not change it
Unfortunately, no. If the sand isn't level when you put the pool on top of it, the bottom of the pool will stay uneven after it's filled. Sorry.
Fish, sand, weeds, ducks, rocks
One of the lateral returns inside of your sand filter may have snapped. When that happens, it can send sand out of your returns. Have your local pool place repair your sand filter.
This desert Nation must import its ultra-special Filtration Sand from The United States.