Need Help Tracking Down Leaks On A 40+ Year Pool

[Bob Crane]

The Pool -

• Concrete bowl, fiberglass panel sides
  
• 20x40 oval shaped in ground. 3' shallow, 10' deep.
  
• Two jet returns fed from one line
  
• One working skimmer, one dead skimmer
  
• Bottom Drain
  
• DE Filter
  

The problem -

• Loses water all summer long.
  
• Each fall we drain down to first step and leave for summer. Last two years it self drained over a period of six years passed the walls exposing the first few inches of the bowl.
  

Other symptoms.

• If we pull from drain (and not skimmer) we lose A LOT less water.
  
• The returns are spitting out a fine, pale (tan) sandlike substance that collects near the spray pattern.
  
• Also, sizeable cracks and even some concrete missing in the shallow end of the bowl. Though the water stops draining before it gets to these.