That seems excessive for such a moderately sized pool.

Why do you think you have to backwash that much?
Is your pressure rising that much each day?
Normally I backwash when my pressure rises from 20psi to 25psi.

Did you fill your filter with pool filter sand? It comes in 50# bags specifically marked "Pool Filter Sand". If you didn't you should replace the sand with the proper stuff. It's not expensive.

However, when sand is new there can be a tendency for some to come into the pool for a little while.

OK. now let's assume that there's nothing wrong with your filter. You said you had to change the Intex filter every 12 hours--and whether you are washing them or replacing them, I agree--that's far too much. But if they are clogging that much then it's because something is falling into the pool.

We've had a ton of pollen this season--I use skimmer socks and they constantly come up caked with pollen. If you are in the NE that may be part of your problem.

I also hate to say this, but your pump MAY be a little small for the task. I don't know the HP on it but usually for this size pool a 1/3 to 1/2 hp pump is perfect. But let's rule out all the other possible causes first, before we go spending your $$$!