What Am I Doing Wrong?!

[Synirr]

I have a Magnum 350 canister for my 80 gallon, and have gone through 3 impellers in a little over a year. What on earth am I doing wrong? The first two were my fault, I admit. I put the intake too close to my sand and one of my fish would spit sand into it while digging so the impeller got scratched up, but this problem has been rectified. Today I cleaned it out as it was a little clogged and immediately after hooking it back up and "burping" it, it started sounding funny. Sure enough, the impeller was a little scratched. There was NO loose debris in there whatsoever, and I am gentle as a lamb with that thing because I'm terrified of making it sound like a jackhammer again. It is on a completely level surface. What the heck!?

I either need to figure out what I'm doing wrong or buy a couple of HOB filters or something that I'm less likely to break

 

[WILDER]

Sand is bad on impellers are you switching the filter of during a vac.

 

[timmystood]

Make sure the water level complety covers the canister filter before switching it on.

 

[Synirr]

I don't switch off the filter during a vac, but it's because the sand near the intake never gets stirred up and the water level never gets below the intake. I switch it off when I am stirring the sand

 

[Durbkat]

Maybe the filter is faulty and is ruining the impeller or one of your fish are biting it and scratching it up.