Thanks for the replies, I realise this too - I have one canister filter at the moment but if I find I can add a ray I would buy a 1000 gal/h pond filter + pump.
I've had my tank custom built because 3ft is my limit in length so I needed the 2.5ft width, it's 36"x30"x18", from what I read the height of a ray tank is not important and the minimum width is 2ft so that should be okay but i'm not too sure about the length.