Hi, Hoping someone can help me, new to this site and to keeping tropical fish. Have what is about a 40g tank (well thats what all the calculators tell me from the measurements) and it is now ready to add fish (FINALLY)) I initally wanted guppies cause i thought they would be easy and are quite cute, but then decided i want angels but found out they would eat the guppies. So i have started out with 6 black widow tetras. Now i have decided i want a black ghost knife fish. Is this a suitable option? And what other fish would go well in here? Any suggestions and advise would be much appreciated.