Thing is though...you may get conflicting advice, but that's because some is correct and some isn't.
I mean there is some room for movement as fish are living animals, so you do get exceptions to the rules every now n again.
But in response to Silky's advice, his/her tank is 125l (I read through past posts), it is grossly over-stocked. Unless they have a huge canister filter then they will run into water quality issues very soon. Also unless it's heavily planted the the nitrates will sky rocket between weekly water changes.
Alot of the fish will not be comfortable in that tank long term (particularly the rainbows + plecs) and are also not being kept in the numbers they should be kept in.
AND they have a post named 'My red tailed black shark is being aggressive again'....
So my point is, think twice before readily accepting someones advice. Make sure they are a knowledgeable person by looking at their own tanks.