I build my own tanks so can't answer your question directly, but when I make mine I mark the variouse tubes with my sciber. That way I don't forget and yeah....I forget more times than I remember! LOL If you have done any soldering at all, it is a very easy matter to remove the back (as Bootlegger suggested) and see what each tube is, then replace the back. Not much help I know, but I hope this helps.