Took me a bit to recall as this all occurred at the beginning of the year around February. This is what I remember...I was advised to use API Quick Start by the store I purchased the fish from and Amazon extract. I used the 'Quick Start' to start the tank up. My pH prior to the purchase of the fish was continually rising to around 7.4 - 7.8 so I was using pH Down throughout the three weeks and nitrate down etc. I could go on and on as I was testing the water every day and in and out of the pet shop with water samples; going home with new products (all on advice from the store). The store was insistent that I had to get my pH to the magical number of 6.8. I think now, with the later advice and reading of the docs from the website you put me onto that I just didn't give the tank time to cycle well enough plus it was an over buffering of chemicals. My tank has been continually running now since the loss of the discus and my two corydoras are as happy as larks. I purchased a 150 litre tank and a RO system (which I've yet to run). I was considering just trying again with just my bore water rather than going to a combination of bore and RO as being able to just do wc from the tap would be a lot easier. in terms of the water hardness that I posted at the beginning of my post for help - do you think the fish would adjust to this hardness or would I be better to install the RO system and use a combination of RO and bore? I haven't read your link on cycling a tank yet but will do so now. Thanks again for all your help.