yeah read the title its self explanatory lol

Depends what fish - for goldfish which are dirtier than tropicals, ideally you should be looking to pass the volume of water in the tank at least 8-10 times per hour (so 1600l/hr minimum) - an external filter would be your best bet as the outlets can be positioned to cause minimal current even for the large throughput of water.

For tropicals, a tetratec 1200 (1200l/hr flow) is a reasonably economical external filter for 200-500l tanks. I bought mine from The Living Seas (http://www.thelivingseas.uk.com/p/474185/tetratec-ex1200.html) - £63.99 with free delivery, as opposed to £89.99 from shops in Sheffield

(the EX700 is £10 cheaper but doesn't qualify for free delivery so it's only really £5 cheaper, and "overfiltering" isn't something to worry about, so I'd say go with the EX1200)

thank i was jsut wondering what else i would need for a tank thats so big

apart from the filter and substrate what are the other things i will need its for coldwater fish

just thinking itll be a bit different than the small tank i have at the min lol