What I'm saying here is that the "academic code of conduct" is a bit outdated.
Of course tangential to the citing of novel ideas is the citing of material that helps explain your work. I think it's certainly a good idea to cite a source of common knowledge if that source does an especially good job of presenting that knowledge.
As with all things, this is a judgment call. Just try to be honest...
"To solve this discretized Poisson equation we use the BiCGStab method \cite{vanLeersPaperAboutBiCGStab}, which is an iterative Krylov method; see \cite{SaadsTextbook} for a general introduction."
the bibliography is an important part of your work. its there to help an interested reader understand your work more fully by placing it in context, providing more access to a more exhaustive discussion of the finer points, and to assist in their studies of related topics.
at some level thats what it has to be about.