You only need the water crystals if you do not feed any fruit/veggies that are high in water. I started with the crystals and just switched to oranges. Never had a problem.
Also, the food that is offered in the link I provided has a very good mix to it. I think he gives the ingredients on his website. Never needed to worry about anything with his food. (You can use pet food/fish flakes but remember that not all food is the same and may not offer what you need.)
I do want to mention that depending on how you have your set-up will determine how feeding fruit/veggies goes. If you keep a closed container with just some holes for ventilation, the food will decay fast and mold if you do not change every day. I started that way and changed to a screen top and never had any problems after that. The great thing is they do not smell very much (if at all) so unless you have your head right in the tub I never smelled them in the room.

Jim