Romeo,
A few comments/suggestions-
With 150 lbs of play sand as substrate, I would be careful with the stones in your enclosure as uromastyx are terrific burrowers. Deaths have resulted from uromastyx being kept on granular substrate and tunneling under heavy stones and being crushed.
Temperature. I would suggest elevating your basking spot to 120-130F (guideline not a magical number). The cool zone of your enclosure is fine at 80 but it might be more beneficial for your uromastyx if you could keep a fairly decent portion of the enclosure at a slightly higher temperature range of lets say 90-100F. These guys have a preferred optimal body temperature well above most other animals so attempting to provide them a comfortable roaming area within lets say 10 or so degrees of this estimated potz (under-not over) will allow your uromastyx to be more active and utilize a better portion of its enclosure without the need to constantly sit under a basking light. A good predictor of whether you are doing this right (in addition to a digital thermometer) is the animals behavior. You want Yoshi fairly active during the day. If he basks a lot, you may want to try upping the gradient temperature while paying close attention to keeping a large enough cool zone for him to effectively thermoregulate.
UVB. You mention that your enclosure is 24 inches tall and that you have installed a Reptisun 5.0 lamp. Unless you have manipulated this much, much closer to Yoshi, I have my doubts about how beneficial this bulb will be. I have been testing uvb lamps for some time now and have not found a standard tube uvb bulb that puts out adequate amounts of uvb at 24 inches. Most of these bulbs have considerable decay within a month of use so if you can mount this to within 10-12 inches, I think that the bulb will be much more effective.
Diet. My recommendation would be to use 2-3 staples and supplement with a variety of greens. This will allow you to introduce a diet that varies a little in nutritional composition. As we do not know the exact dietary needs of a uromastyx, this will reduce the possibility of us focusing heavily on one or two items and possibly missing out on an important vitamin or mineral necessary for optimal health.
My personal preference would be to limit the animal protein but I doubt if anything harmful will result from feeding a cricket once per week. If you are feeding heavily once a week, you might want to do a little research on how animal protein has an impact on the health of herbivores and how quite a few in the field/hobby are under the belief that many uromastyx are true herbivores.
The reason you might be seeing an excess of white stuff around Yoshi’s nose is that dandelions are rather high in sodium compared to other greens. Adding a few other greens to your mix rather than focusing heavily on just dandelion should help with this.
Uro dust. If you are using T-Rex Uromastyx Dust then I personally do not see a problem with using the dust every other day or even sparingly daily. This product contains a much smaller percentage of fat soluble vitamins than most vitamin supplements on the market. One really needs to look at the diet being fed and the analysis of the product when determining how to correctly supplement as they are not created equal. Just compare several of the primary potential problem (say that 3x fast) vitamins between T-Rex Uro Dust and Zoo Med’s Reptivite. Uro dust contains roughly 20,000 IU of vitamin A per kilo wheras Reptivite contains roughly 220,000 IU per kilo. Uro dust provides vitamin A in smaller portions due to the possibility of toxicity but then adds in a source of beta carotene for those animals that can convert vitamin A from this resource. (Some manufacturers have introduced products that ‘only’ provide beta carotene rather than vitamin A but I am not so certain how effective ‘all’ reptiles are at converting beta carotene to vitamin A so I personally like T-Rex’s route of providing a small amount of A and the beta carotene) Also compare the d3 levels of the two products. T-Rex Uro Dust contains roughly 4000 IU of d3 per kilo while Reptivite contains roughly 22,880 IU per Kilo. (These are estimates as I had to convert from pounds to kilo and the analysis therefore will not be as accurate) I am not pointing out the difference in these products to promote one over the other- just to show that each product needs to be looked at individually when determining how much to use. I certainly would not use these two products equally.
