i get feedback all the time of folks taking the 50/25/25 mix, and then adding their own materials to it. cypress, bark, calci sand, bed a beast, what have you.
and then it becomes a substrate mix that doesn't work so well : )
the 50/25/25 mix works, because it does. it is like the existence of the Universe. you can't just say, i wish gravity was 8 times stronger, and expect everything to be the same 
if it needed other ingredients, i would have listed those. it works as it is because it allows for the basics. digging, burrowing, and water retention. the "change" that you can make is your exact ratios. take the three ingedients, and add a litte, substract a little, so that the mix in your very hands is doing the right things.
but still folks insist on adding stuff : )
adding bark will break your bind. it won't dig as well, and it won't burrow as well. the vermeculite is there to add ADDITIONAL bind as it is. adding some large particle ingredient only works against that.
many folks like to add bed a beast. once again breaking the bind. bed a beast, for lack of a better description after climbing out of bed this morning, is too soft and fluffy. it will reduce the hold of your burrows. that's NOT what you want to do.
now, adding a layer of bark OVER everything else, that's an ok idea. with monitors, a lot of keepers add a layer of leaf litter, very successfully. i don't know WHY you would want to add a layer of bark, not sure what positive purpose it would serve, unless you just have a ton of it around and need to use it. but it shouldn't hurt the situation, and should react very little with "the mix". i think once the animal starts actually digging, the bark is going to be a mess, but you could pull it out at that point, or not add it at all.
ONCE AGAIN (for the general forum) you don't HAVE to use the soil substrate, not at all. i would love to see you try, but REALLY, you gotta kinda stay in the outline. it works in its own configuration. not just any dirt will do. you can't make a succesful soil substrate based cage by being lazy. you can't let the Home Depot guy talk you into using potting soil filled with all kinds of stuff, when you are there to get topsoil, sand and vermeculite. ("but he said potting soil was the same thing, it already HAD all that stuff" really?!? is he a lizard breeder? : )
REMEMBER! the store bought mix is the ALTERNATIVE! the best soil is going to be the one you dig yourself! not every soil will work, you STILL have to get out there and find that streambed, or forest, prairie dog town, or backyard with a good, workable soil
and good grief, don't give up after one week! i see that some folks have gotten frustrated, but the end result is WAY worth it. it is going to take a couple of months just for YOU to start learning about how the soil really works in the cage. all you can do in two weeks is get your fingernails dirty : )
better growth and better HEALTH is our (PE) result at this point, and this has been fedback by a few other forum members that have made the jump. all signs point to long term results along the same lines.
so you can achieve better health with a better setup. what is the opposite of that? well, the current accepted Uro standard and setup, which logically means POORER HEALTH. and as reptile lovers and hobbyists (this is not a "breeder only" goal) that should be amazingly important to us all.
i know i am new here, and i know there is a lot to absorb from what i am saying. and i know some "big names" have dismissed the ideas a bit (without investigation?) but still, Pro Exotics is a successful monitor breeder, a successful lizard breeder, and i AM looking at the Uros critically. i am not here after a ten year run in the cornsnake forum, now trying to tell you guys how to live life, that you're dumb, and i dreamt of a new way to keep "Uromatchstix", we have been through the trials and tribulations with the monitors, and i see only positive Uro feedback when i apply that same theory to the Uros. lizards lizards lizards, apply apply apply!
thanks for hanging in there, as always, i enjoy the feedback and exchange, and we continue to push forward for successful captive care and reproduction of the Uromastyx!
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robyn@proexotics.com
Pro Exotics Reptiles
