Axolotl isnt eating.

Hey,
I am a bit concerned because my black axolotl, Bob, isnt eating. It has been two days now. I understand that they can go for several days without feeding food, but Bob has always been keen for a feed and all of a sudden he is just refusing my food. I feed him pieces of raw prawn which i wash in fresh water. He has been on them for 2 weeks now and never a problem. My other axolotl, Marley, seems fine and is still eating. The temperature of my water is normal and i have been maintaining my 20% water changes. The pH is a bit low...it is about 6 at the moment.
What should i do about Bob? I was thinking i would wait another day or two and continue to try feed him. He isn't showing any notable signs of a fungal infection or anything so I am unsure whether he is actually sick.
Any advice is appreciated. Thanks

When you say his pH is at 6 "at the moment" do you mean that this it's usually at a higher lvl? Changes in pH could be a stress. However if he's been living in such water conditions for a while the pH may not be the problem.

I don't really know about the raw prawns. I'm sure others on this site will be able to tell you more...have you tried feeding him something else? Perhaps something wriggly like a worm?