i have just brought a 4 ft tank for my single oscar... and i dont think my little filter i have now is anywhere big enough for the new one...

any suggestions on what kind of filter system i should get...

i'd go with a fluval 204 or 304

in my opinion you need at least a 305/405 and try to get a system that runs two externals if you can as oscars are realy dirty fish and you will see toxicity levels rise much faster with o,s than other fish plus you always got a back up filter

the size of the filtration you need is directly related to the size of your tank. now you said your tank is 4 feet long but how wide and tall is it? i have a couple of 4 foot tanks and one is 40 gallons and the other is 90 gallons. obviously the 90 gallon tank will need twice as much fitration as the 40 gallon. if you can give us your tank measurements we can give you a better idea on how much fitration you will for your oscar.

also if you wish there is a link on the home page of this site which will calculate the volume of your tank. all you have to do is enter the dimensions