size of pump needed for Hayward S160t sand filter

I am wondering if anyone knows what size motor (pump) I should use for a Hayward s160t sand filter. When I bought the house, the pump worked the first year and then crapped out. The labeling on it was so sun baked, I could not read anything. I knew it was 120v circuit, so I just bought the largest pump that would run on that circuit (1 and a half horse). I have not been able to get crystal clear water since. I just replaced the sand in the filter and there was only about 100 pounds in it, I found several pool sites that said it should have 150. Also 150 brought it right to the top of the clam shell. Well, when I first backflushed it, it shot a bunch of the sand out the waste. I'll bet it's down to 100 lbs. again inside and I still can't get clear water. Any help appreciated!
 
I have a 32' by 17' in ground pool. Cement or Plaster, not sure, it's an old pool. It is only about 2 and a half feet deep in the shallow end. I can sit down and still have my shoulders and head above water. Of course, I'm 6'3". The pool is only 6 feet deep in the deep end. I can stand flat footed and it almost covers my head. Nearest I can tell, it is about 12,000 gallons. I determined that with a calculator I found on a pool site. It has one drain pipe and one skimmer (2 and a quarter PVC) and two return to pool valves. Anything else you need.