yep, I'd be worried about the running cost of using that spa pump if I was you. At a rough estimation, a 700W running 24/7 is going to cost about $110 dollars a month to run (assuming 21.5c per kWh).
At that rate its not going to take too long to pay off a new pump that uses less juice. My 90W pump (Resun King-4) does around 3000L/H at 2m of head, it only cost NZ$121, and I am using it on my 1.6m*0.6m*0.6m tank to run my DIY trickle filter which provides plenty of filtration.