concrete coating repair on old pool

I have a +50 year old pool with concrete bottom and fiberglass sides, the bottom is flaking off with stone aggregate exposed on roughly 20%, more or less. I believe this is where I'm losing aprox 1/2"-3/4" of water a day? I had all the lines tested and fixed. I have several thoughts on what action I should take and would like to know of other peoples experiences and recommendations. I'm relatively sure I will sandblast 1st then the options would be
shotcrete to smooth and thin coat - pool paint?
ultra guard ?
sani-tred and pool paint?
other suggestions?
hoping for responses from people who know 1st hand what has worked and what hasn't with a few years of time on it. thank you Chas from PA