Big Enough Filter ?

In a tank that size an external filter would be better. But the guideline for filtration is a turnover of at least 5 times the tank's volume for hour for an unplanted/lightly planted tank, and at least 10 times for heavily planted. The flow rate of your filters should be in the manual somewhere but bear in mind that it will be less than the figure they quote. I know that with externals most companies quote the flow rate withour media inside the filter, and the real-life flow rate with media is a lot less. Internals might well be the same.

Thanks peeps, one for the xmas list then as my tank is lightly stocked with no Plants just rock and bogwood.