you have to stay on the sell fish page for about ten minutes until they sell, you cant just put them in and expect them to sell when you go back to tank one...did you know that when you sell the fish you can ask whatever you want for them? when they are in tank one put them into the ickle tank at the bottom and click on species, there's a calculator at the top right hand side and you just put in how much you want for the fish before you put them into the sell tank
and dont forget to get them pregnant by putting two fish (doesnt matter what species, mix them if you want) into the ickle tank at the bottom of the page...i do that then sell the one thats NOT pregnant