I had gold fish as a child and when my children were small my husband decided to get my daughter a fish, we went to the store bought a tank asked how many fish it would fit went away set the tank up and a few days later we went back to buy the fish. Now when I was a child it was a plastic bowl with a coloured rim and feed it once a day so when we were told to use filters and such like we were shocked but duly did so. No one explained goldfish would soon out grow the little tank needing larger and larger ones, we trusted the store. We started to look on the internet and we realised that we needed to put them into a huge tank or a pond we duly did so.
When I started looking at tropical fish I visited many sites and there was a lot of conflicting information, it is through a lot of reading and research I have discovered that almost everything all the different stores I have visited have told me is wrong and each store says some thing different I was told in one I could fit 20 guppies in a 60l tank with 3 platys and 6 neons

oh and a common pleco.
Each on line calculator give out different information, each website differs, fish are not recognised or protected, we know that people who have 16 cats or 8 dogs are slightly in need of help but no one thinks about fish in the same way, think back to childhood tanks, the staff in fish shops should know their product but then the staff in Asda don't know where the cleaning stuff is never mind if it is suitable for sensitive skin but we can read that on the packet, it may need to be made law that tanks are labelled such as Platy, tropical, live breeder, needs x amount of space (or needs x litters of water per fish) male to female ratio, then warnings, each fish could be given a colour or 3 so green fish can only go together or red fish and you must not mix colours. If each tank was labelled correctly then the customer could be held responsible, each store would have to abide by the code to sell fish. Sadly this will never happen.