Thanks guys! The 'playpensand' I have seem pretty coarse, will go and have a look at swimming pool sand to compare.. At the moment I have very fine mozambiquan beach sand in my 200l tank, but can't get the water completely particle clear.. It is driving me nuts! So I'm going to transfer the occupants to a 250l tank with better substrate. Will pm Prof. Dirk and hear if he can help with ferts. Currently using Kent freshwater plant every week. Thanks for the advice, really want to get the new tank right first time around! Does the silica sand affect the water chemistry in any way?