I am having trouble developing my rolls of film. I have had two casualties today. The first time I developed 3 rolls at once with one liter of solution, consisting of 250mL of Kodak D-76 to 750mL water for 19 minutes and obviously this was a mistake. The roll on the bottom of the tank was transparent with no visible leaders along the sides. While the other two were just fine. I did research online and many people said that the transparency was due to lack of developer, and so I recalculated and decided it would be smartest to do 2 rolls using 500mL stock and 500mL water for the same time. Regardless, The bottom row still was transparent. I am really confused as to what I should do, and obviously hesitant to continue developing with out advice from others.
If the film is completely transparent: no numbers on the edges and, critically, no fogged leader, then it has never seen the developer. But it has seen fixer, or it would look like undeveloped film (possibly with the anti-halation layer washed away), which is kind of grey (and will get darker over time as light hits it).
As Alan Marcus says, if the leader is fogged and there is edge printing, then it has seen the dev & there's a problem with the camera, or it's never been in a camera.
It's hard to see how the completely transparent case could happen, especially for the bottom roll in a tank. If you are agitating by inversion then it really can't happen I think as some chemistry will get on all the films even if not evenly. If you're agitating some other way then it's possible for the top roll in the tank to be partly or completely out of the dev, but even then it's hard to see how you would not get splash on it when agitating, and when filling and emptying the tank.
If the film has seen any dev at all (and was exposed) then there would be some image there: it might be very pale, and it might be partial if it is from splash, but it will not be nothing. Your reported dilutions and times (the first one) look fine for D76 for common emulsions: obviously things vary to get the best negs but this is ball-park OK: there would be some reasonable image.
And also, we know it saw the fixer: how can that work?
As described I find it very hard to see how this could have happened, unless the film has never been coated in emulsion or something: that should be detectable by looking at the film: if there's no emulsion both sides will be shiny. It is possible to wash the emulsion off film, but you need really hot water to do that, and even then there would be fragments left.
It would help if you gave details of the tank, agitation &c perhaps.
You say, the bottom roll was transparent -- look at it again and tell us if you see any edge printing. 1. void of any image or blackening whatsoever even the edge printing with frame and emulsion type missing top and bottom. 2. Edge printing one side of film only. 3. Edge printing both sides but nothing else.
Edge printing is photographically applied and develops up with your images. If edge printing is present, then we must suspect the camera or the roll never advanced etc.
It has been many years since I developed film, but when doing so for myself, I always did one tank at a time, with just one roll per tank.
I am not saying this is your problem, but when pouring through multiple rolls of film, it is possible to loose consistency in agitation and that could cause problems like this.
Finally, you are diluting D-76 more than what is generally considered optimal for sharpness, which is a 1:1 solution. It is been quite some time since I used D-76 but it is possible that the low concentration of D-76 without replenishment, and with less agitation at the bottom of the stack, might have a contributory effect.