Dude the larger fuse wont give you any problems, it just wont blow, but its not supposed to either. That fuse protects the wire, the ones one the amp protect the amp. Go figure.

 

weird....sounds like a bad connection/short somehwwere

also a 150 amp fuse would be a better choice

 

You are fusing according to the wire not the amp. 250Amp fuse will be fine for 0 gauge wire. The fuse is not the problem, as already stated.

 

100% definitely not a fuse related issue, a amp only draws what it needs not what the fuse is rated for up front. The sole purpose of that fuse up front is to protect the vehicle from damage (fire) in the event of a short circuit on that main power wire.

To me it sounds like you have a super duper bad ground, the wrong size wiring being used on both the power and ground or as correctly pointed out earlier, a defective sub.