well first, does it run off 12v dc or standard ac current (plugs into an outlet)?
if it runs off 12v, you'd have to hook it up to your psu so it would turn on and off with that. the only way you could have it turn off with standby though was if it was hooked up to the cpu fan header and your motherboard supported turning the cpu fan off in standby. but that might short out the motherboard so it's not such a good idea...
if it runs off ac current, you can setup a relay switch to turn on and off with your computer. or you could get
this, which turns on and off the outlets when the main outlet draws current. it works well and i've used it with my setup...
however, for the most part, these pumps are designed to run 24/7 and it's a good idea to let them do just that. it might even be worse for them to keep turning them on and off.