Hi Matty,
Before tackling anything else I really want to say that you obviously have a natural gift for landscaping in miniature. The elements you have chosen and the way you put them together is brilliant - I love it. It takes a lot of time, trial and error and most of all, talent, to end up with something that looks that good.
Suprisingly the humidity levels are not as consistent high as I would have expected given your initial description of what was done. This and their daily variation suggest to me that you have a lot of ventilation. While not a bad thing in itself it can affect the stability of the temperature gradient. But again, it depends upon the non-moving air pockets that exist in such a complex arrangement.
Tropical fish have been artificially selected over many generations to obtain individuals with lower temperature tolerance limits than wild types. Artificial selection is one of the main processes that has produced the varied traits we now observe in domesticated animals. There is no reason it cannot also be applied to repltiles. However, be aware that a generalisation it large numbers to choose from, selective breeding and quiet a few generations to achieve the desired results.
Despite what much of the net will tell you, Hoya carnosa is not native to Australia, although it has become naturalised in some areas. It originates from southern China. H. dischorensis is not a recognised botanical name and looks like something the trade may have invented. They sometimes do that for hybrids by combining parts of the two species names. Whatever, I can guarantee it is not native. There are about 10 native species and I have only ever seen two of these in the trade - H. australis and H. macgillivrayi, both of which require good light. There are some excellent small leaved exotic hoyas available.
My own preference for lighting would be one or two full length fluoros, the same as you would use on a freshwater planted aquarium (such as Growlux). These produce more light in the red and blue ends of the spectrum than other lights, which is what the plants need. The blue end in particular will encourage bushy growth rather than lanky (etiolated) growth.
Don't be afraid to get in there with the scissors on a regular basis. Little and often is the way to prune most vivarium plants. With those plants that have large, long leaves, take any excessively large ones off at the very base. Don't fertilise until absolutely necessary and this will help restrict growth.
If you look a distribution map for U. milii, it indicates that they are not that keen on the higher humidity areas. In dry eucalpyt forest bushland around Sydney, you may find them on north facing slopes but not on the moister south facing equivlent. From my experience they will utilise bare rock crevices or take refuge under rocks or logs on soil which almost dry but I have never found them on particularly moist soil, let alone wet soil. I would go for a drier microhabitat.
A. leuseurii seem to prefer exfoliated rock slabs in my experience. I kept a colony of half a dozen for several years. I had a stable stack of three flatish sandstone rocks in one corner and some coarse silica sand with a few rock pieces as the substrate. Plus a couple of pieces of dry wood. They had a small water dish. Probably once a fortnight I would flick some water around off my fingers - they did not have spray bottles back then. They were fed with whatever insects, spiders, slaters and other ivertebrates I could catch in the garden, plus a few mealworms. I used to catch bushflies using a large aquarium net, put them in the fridge and then remove the wings once they were slowed down. These were very much a favoured food. Sorry about the rambling. Yeah, definitely on the drier side for these guys.
Christinus seem to have a wider tolerance as they are seasonally exposed to high humidity as well as dry periods. I would not want to keep them in continuously high humidity. Definitely not one to keep in wet conditions as they shelter in rock on rock, bark on dead trees and the eaves and ceiling areas of houses.
You could probably put together a rock (with some wood) landscaped viv that would be suitable for the A. lesueuri, U. milli and C. marmoratus, so long as they are similar in size. U. milli will eventually need to be separated before they get big enough to make a meal out of the other inhabitants.
A drier planted viv can be made by having a thick layer of substrate, usually low in front and deep behind. Place place round plastic containers without holes, such as small yoghurt or margarine tubs, so that the top of the container is level with the substrate. Use round pots that will sit neatly into the containers. Cut the pot down to size if to fit level with the container and remove some soil from the bottom of it, if needed. You can also make your own pots to size. For example, take two small youghurt tubs, stack one inside the other and cut off the top to the depth required. remove the upper tub and cut or melt drainage holes in the bottom and use the plant pot.
The plants should be watered by removing them placing in water for half an hour or so to saturate them. Then drain for 5 to10 minutes before replace in terrarium. Use of leaf litter around pot tops will obscure the potting soil and plastic container. Plants can be cycled with a replacement kept in a shadehouse. Simply alternate as required. In this way, plants not particularly well suited to long-term vivarium growth can be successfully used.
Some other species that have not been mentioned but that I would think should be well suited to your existing vivarium are...
Pinktongued Skink, Major Skink, young Water Dragons, Southern Angle-head Dragons, Eulamprus species other than the mentioned Water Skinks, such as tenuis and tigrinus, The *****kly Forest Skink, Carlia species such as rubrigularis and rhomboidalis, the Giant Tree Gecko, the Iron Range Ring-tailed Gecko, and smaller, less frequently kept moisture lovers such those in the genus Saproscincus.
Blue
