I cleaned my filter grid's today. I have it all put back together and when I put the clamp back around the unit it will not reach the top and bottom to clamp back on. What should I do? I bought a new o-ring thinking that was it and it still will not clamp around.

If you actually had any of the filter sections out of their place in the housing its likely you don't have them fully seated. Does each section look like it is fitting as deep as all others?

Yes, everything is down to the bottom and level. I checked because I thought that was the problem. I had it closed for about 30 minute's while the pool was running and then it popped off and water gushed out. The clamp goes over part of it but not all.