You could try this
http://www.fishandfins.co.uk/stress-zyme.htm
I use this and it does help to clear the tank,I use water from the pond for weekly water changes so its quite murky at first,it clears but still has a tinge of colour to it.I have gravel and a few plants in, but dont want to remove them as I think its nicer for them to be able to root around for titbits of food
