THANKYOU ALL.., I really value your advice and i will do everything you all said, ''more questions'' .....how much of a gap should there be at the top of the tank to the top of the water? also i read some where as im waiting 24hrs before i put the fish into the new tank water that i should squeeze the sponge out of the filter into the water to give it some't or other.., is that true?...also ive gone with having NO gravel what so ever at the bottom of the tank as it was dis-colouring the water , what else can i use that wont dis-colour the water in any way at all? Can i use them different coloured glass small pebble'y things? SORRY to ask so many questions but i dont want my fish to suffer or die. Also here are the exact measurements of the glass tank,which is a funny shape..:- Length=18 inches,or one and a half ft..Height,or Depth=15 inches and Width=12 inches with a 3 inch roof space. Surely thats adequate for the fish i have? The fish that are going in this tank is ''1'' 4inch gold fish...''1'' red and white koi..and ''1'' 1inch shubunkin.