reellis67 said:
...I think that most people have their own opinions about how much grain is too much, or too little so you may find a bit of experimentation is in order...
Herein lies the crux of the matter, in my opinion. Your question is a valid one, but it is difficult to answer "properly" without quantifying various aspects of it a little bit more. I know that the ability to do that comes largely from experience, but I think you will get better help if you can provide a bit more informations, such as:
-when you say "too grainy", do you mean compared to other films of that speed(400)? Or is it a matter of just not living up to your expectations as far as grain is concerned, period?
-have you been able to get better results from this film or others (if so, which ones?) before or on different occasions?
-try scanning a print if possible and posting it - while the transformation to pixels is a very flawed way to view a print, it is better than nothing for our purposes.
Without that info, I can only say that I have used HP5+ a fair bit, and it is not my favourite 400 speed film but only due to personal taste and matters of appearance rather than any fault of the film. Actually, since I prefer the traditional emulsions such as HP5 and TriX, and don't want to hand over any more cash to Kodak, I have picked up HP5+ more of late and am trying to find a way to get it the way I want it - and I have to say, with some work on my behalf, I am finding that a large part of what I didn't like about the film was due to the fact that it didn't do it for me "right out of the box" and instead of trying to find a way, I found different films. Now, with some work, I see plenty of potential - and again, keep in mind, that this was always a matter of "I prefer film x" rahter than "HP5+ is a bad film" for whatever reason.
As far as grain, I find that HP5+ has a distinctive look that you either like or do not like, but the size of the grain is by no means out of line with other 400 speed films of this type (for example, I found the - now defunct - APX400 in its last iteration to be just flat out more grainy than others and even I found the grain objectionable, especially in 35mm - not the case with HP5+).
Then again, I am a guy who likes grain - I feel it is akin to the brush strokes and texture of a painting - so please keep that in mind also. That and the fact that I like almost everything in Rodinal...
Well, once more, I have written an essay - sorry about that!

Try to post some more info and along with more explorations and experiments on your behalf, I am sure we'll find a good solution.
Peter.
PS I recently souped a roll of 35mm HP5+ (shot at box speed) in Acufine, and found the results to show a lot of promise, relatively fine grain beingone of the results.