The "gritty mix", AKA Tapla's medium, is very heavy due solely to the grit component. He commonly recommends granite (like Gran-I-Grit), but a lighter grit can be subst without concern as long as it doesn't retain (much) water internally, inert, doesn't breakdown easily and most importantly is the right size (~1/16"-1/8") and shape (not perfectly spherical). If you're concerned about the weight, even sifted Perlite can be substituted for the grit component.
I'll go out and weigh some of it dry and wet tomorrow. Although I'm not sure it will help you because mine is heavier than most. For my arid zone, I use a more water retentive version of the gritty mix by adding 20% more Turface (or Napa), using a smaller #10 grit, and sifting both using a smaller insect screen (1/16x1/32 rect holes vs. 1/16x1/16 squares), though I still sift bark using traditional screen. My modifications were done with Tapla's guidance and are slight enough to still avoid perched water. It is a heavier mix (though still fast draining) especially when wet.
The young citrus do *excellent* in this mix and it's nearly impossible to over-water. However, I have not tested it with mature citrus that bear heavy crops. I've some possible concern over that, due to some recent experiences with bearing nectarine trees in the mix. But I cannot say yet it's the mix's fault.
