Advice On Filter Setup

With that size tank an external is the better filter type. But which one depends on how much you are willing to spend.
Eheims are the most highly rated so of course they are the most expensive. Don't get the eco versions as their manufacture is outsourced and they are reputed to be not as reliable as the other types which are all made in-house.
Fluval is another good make, but again expensive.

Cheaper options include All Pond Solutions which are fine as long as you bear a couple of points in mind. They are made from thinner plastic than the dearer makes, so be careful handling them. And their flow rate is a lot less than they quote so go for a higher litres per hour turnover than you'd assume you need. (They are one of the makes that quote the flow rate of an empty filter, and as soon as you put media in it, the rate drops off considerably)

Hi Joe, I have an all ponds solution external filter and it works fine on my 250 litre tank. As Sue says though the flow rate is lower than they suggest, however with slightly more up keep my flow rate stays at a nice rate, I also moved and tried different filter media until I had the flow I wanted. I've had fluval externals before and they are ok too but my external cost £50 new which is around half tHat a fluval and does everything that a fluval would do.