With your gelatin and dichromate, you should be dissolving in about 35 mls of water. However, most dcg holographers us ammonium dichromate, not potassium. Potassium dichromate is less sensitive than ammonium dichromate and you need a longer exposure than you'd normally use. As a rough estimate, I'd use about 30 to 40 mJ/cm² for the ammonium salt, and about 50 to 60 for the potassium. The fact you may be under-exposing may explain the dim images.
How do you pre-harden before the water wash? You may be pre-hardening too much, which would explain the blue image.
One thing that strikes me is the stability of the mirror. If you gently hold the mirror and gently twist it to-and-fro, it should not rotate. If it does, you need to tighten the mirror. You could also hit the mirror with a raw beam (un-expanded) and tap the mirror. If the reflected raw beam moves, the mirror needs tightening.