hello,
Im pretty much a newbie too, but Ive been researching. and for your tank being a week old, it seems that you put in too many fish. to start off the
nitrogen cycle you should have introduced one fish. (the scout) the water is not aged enough that the beneficial bacteria needed to break down ammonia in the tank is needing to play catch up with all the ammonia from too many fish. try adding in some beneficial bacteria sold at the pet store like Cycle. Its actual bacteria, it helps speed up the nitrogen cycle. hoped it helped and good luck!!!
