Definitely give them as much hay as you can! Hay, hay, hay, and more hay! I'll admit I overfed my boys pellets (they were being fussy and only taking the tastiest bits of hay, leaving the rest, constantly begging for pellets, and I gave in because I was worried about them not having enough food... big mistake) and their poos turned very dark and smelly, and one of them got impacted. It made me panic! I reduced the pellets, refused to let them be picky about hay, changed the way I give them hay (no more huge piles, but frequently topping it up so it's constantly "fresh" and more appealing and exciting) and their poos stopped smelling within a couple of days and are now very healthy looking, and the one that had the problem is now fine (vet check, and I check him every day). I actually reduced the amount of vegetables, too, because I realised I was giving them too big a portion size.
What vegetables do you give them? Sometimes it helps to get vegetables that will last longer in the fridge. I can get spring greens (they have a slice rather than a whole leaf), green beans, and little gem lettuce, for example, and that will last me for over a week.
