You said..."His main symptoms are inability to climb for long periods of time and lethargy"..."he has had all sorts of troubles walking and climbing"..."He keeps grabbing his front legs with his back legs, tripping and then falling"...."I will find him on the ground"..."he doesn't move nearly as much as he used to"....these are all signs of calcium issues (MBD) as was already said.
You said..."I dust ALL of his food with a ZooMed Vitamin Supplement and a Fluker's Calcium Supplement that has D3. I generally gut load with oats, carrots and potatoes"....as was already said, you don't need to give it D3 that often. D3 from supplements can build up in the system so its better to give it only a couple of times a month and let the chameleon produce the rest from its exposure to the UVB from a proper light.
You said..."It sits on top and has two full-spectrum bulbs in it that I purchased at Lowes. The cage also sits under a sky light, so he gets natural light as well"...the light from the skylight will do no good if it passes through glass or plastic. As was already said....the Lowe's bulbs are likely full visible spectrum not including UVB. However...it seems kind of strange to me that with the D3 you've been giving it in the supplement that it should be having calcium issues. However you said you dust with ZooMed Vitamin Supplement and a Fluker's Calcium Supplement...if its Reptivite that you are using it has preformed vitamin A in it and that may be preventing the D3 from being used to absorb the calcium.
I would recommend that you take it to a vet ASAP and he/she can do some tests to see what the calcium levels are and if it is indeed MBD the vet can give it some calcium injections until the blood calcium levels are high enough to give it a shot of calcitonin to draw the calcium rapidly back into the bones.
You said.."I use ice as a drip system. Usually I put about a dozen ice cube on the screen cover and that drips over the plants I have in his terrarium"...water from ice cubes is likely too cold and your chameleon may not be drinking enough as a result.
You said..."His feces are normal as far as I can tell, firm brown with the yellow part being runny"..the yellow part should not be really runny and should be white...its the urates (urine).
You said..."treated top-soil which I also use as a substrate"...most people recommend not using a substrate. Many of the substrates used can cause impactions so its safer not to use any.
Here's some information that I often post for newbies which will explain bone health and other things that are important in keeping chameleons....
Exposure to proper UVB, appropriate temperatures, supplements, a supply of well-fed/gutloaded insects, water and an appropriate cage set-up are all important for the well-being of your chameleon.
Appropriate cage temperatures aid in digestion and thus play a part indirectly in nutrient absorption.
Exposure to UVB from either direct sunlight or a proper UVB light allows the chameleon to produce D3 so that it can use the calcium in its system to make/keep the bones strong and be used in other systems in the chameleon as well. The UVB should not pass through glass or plastic no matter whether its from the sun or the UVB light.
Since many of the feeder insects have a poor ratio of calcium to phosphorus in them, its important to dust the insects before you feed them to the chameleon with a phos.-free calcium powder to help make up for it.
If you dust twice a month with a phos.-free calcium/D3 powder it will ensure that your chameleon gets some D3 without overdoing it. It leaves the chameleon to produce the rest of what it needs through its exposure to the UVB light. (Some UVB lights have been known to cause health issues, so the most often recommended one is the long linear fluorescent Repti-sun 5.0 tube light.) D3 from supplements can build up in the system but D3 produced from exposure to UVB shouldn't as long as the chameleon can move in and out of it.
Dusting twice a month with a vitamin powder that contains a beta carotene (prOformed) source of vitamin A will ensure that the chameleon gets some vitamins without the danger of overdosing the vitamin A. PrEformed sources of vitamin A can build up in the system and may prevent the D3 from doing its job and push the chameleon towards MBD. However, there is controversy as to whether all/any chameleons can convert the beta carotene and so some people give some prEformed vitamin A once in a while.
Gutloading/feeding the insects well helps to provide what the chameleon needs....so its important too.
Calcium, phos., D3 and vitamin A are important players in bone health and other systems in the chameleon (muscles, etc.) and they need to be in balance. When trying to balance them, you need to look at the supplements, what you feed the insects and what you feed the chameleon.
Here are some good sites for you to read...
http://chameleonnews.com/07FebWheelock.html
http://web.archive.org/web/200605020...Vitamin.A.html
http://web.archive.org/web/200604210...d.Calcium.html
http://www.uvguide.co.uk/
http://raisingkittytheveiledchameleon.blogspot.com/
