keeping a saltwater tank isnt as hard as you think
once its set up and stable very little work is needed as the tank does it for you
for a six foot tank your gonna need loads of live rock maybe £400-£500 and a few good power heads to move the water at least 20 times an hour,the rock with water movement acts a filter
you will also need a big protein skimmer buy one thats rated more than the size of your tank its better to over skim
also when buying your tank try to get one with a sump there a bit more expensive but the extra water helps the tank to stay stable plus you can hide the skimmer,heater in there and put more live rock in it
take it slow is the key with marine tanks,set it up with water and live rock and leave it running for 8 weeks to mature(dont use a prawn or a dead fish the live rock wll crue on its own) then add 1 fish every 6 weeks.hardy ones at first it can months even years to get a good looking tank but the wait is well worth it
oh and you cant use tap water its better to use RO water mixed with a good quailty salt
you can mix it yourself or buy it from your local fish shop
heres a coulpe of sites that i use read read then read some more lol
http://www.marinefish-uk.co.uk/forums/
http://www.reefsuk.org/forum/index.php
hope this helps