A few years ago I had a job finding leaks in swimming pools and I worked on a couple of cinder block pools. Both of them were leaking through the blocks and through cracks in the mortar joints. The owners attempted to solve the problems with hydraulic cements and various sealants and they were successful for a short period of time. One of them ended up filling the pool in and the other hung a liner in it and is still using his pool today.

Not sure about a cinder block pool but the rule of thumb is to be careful with an empty pool and a high water table - the pool can "float". Check to see if you have a hydrostatic valve in the drain - it's designed to spring open and let water into the pool to stop it floating.