Just checked e-mails, and this was in my inbox, should have checked before i wrote my last post

This is the reply from pets at home (uk)
Every store must follow strict procedures around fish care including regular checks on tanks, administering treatments, cleaning and removing any fish that we have sadly lost. We take any reports similar in nature to this seriously and I have forwarded your comments and concerns to the Store Manager and Area Manager of the Renfrew store to look into.
Our fish are supplied to the stores on dedicated insulated and heated vans by our fish suppliers. The fish are bagged in extra large bags with pure oxygen and as such are able to travel for longer periods. The standards we demand of our fish suppliers far exceed those legislated by DEFRA regarding fish transportation.
When the fish come into the stores they are rested for 30 minutes before going into the tanks where all fish will be removed from sale and the lights are turned off whilst the fish adjust to their new environment. They remain off sale until they display normal behaviour usually two hours.
My colleagues would never intentionally sell any fish that is not 100% healthy and any fish tank that is receiving treatment remains off sale until the course has finished and the fish have fully recovered.
Whilst Black Moors can be prone do diseases particularly white spot and the change of temperature or undue stress could have triggered this, without having a sample of your water we are unable to comment further as to why you sadly lost the fish.
The Store Manager was sorry to hear of your loss and if you return to the store at your convenience along with your receipt for the fish they will provide you with a refund. On your return visit please do not hesitate to discuss any concerns or queries that you may have and my aquatic colleagues at the store will gladly address them for you.
Once again I am sorry to hear of your loss and thank you for bringing this to our attention.