Homemade dishwasher detergent

This is so easy you will wonder why you haven't done this before.
The old stand-bys are in this recipe.  Arm and Hammer Washing Soda and 20 Mule Borax.   These 2 things are in so many homemade cleaners.

1 cup washing soda
1 cup borax
1/2 cup kosher course salt
1/2 cup citric acid.  I used Lemi Shine (found at Walmart right next to dishwasher detergents).

Mix all ingredients in a bowl.  Store in an airtight container.  You may have some clumping.  Use a silica packet that is found in so many things such as aspirin to help control clumping.
Use 1 tablespoon per load.
You can also use white vinegar instead of jet dry for spot free dishes.
It is Dad approved.

Thanks Dad for the revised recipe and the research :)

UPDATE:

I've used my dishwasher detergent a couple times now.  No problems.  Dishes come out nice and clean.  The Lemi Shine gives it a nice lemon scent.   I did mention that there would be some clumping.   Mine seems to be one big clump.
Which gave me a great idea.  I think the next time I make this I will spoon my dishwasher detergent into ice cube trays.  Since the mixture hardens together it should hold it's shape.  Making your very own dishwasher detergent cubes.