Wow NICE.
Keep an eye on the Opiophogon Japonicus (fountain plant) near the filter - they tend to rot in the middle and die very quicky, as they're actually a bog plant.
Nice use of the Ortheoceras fossils.
They're well supported at the bottom aren't they?
If Powder takes a mad dash and it comes over, they're very heavy.
Chemically nice and stable however, but be careful about what fossils you put in your tanks, some leach copper and such.
However, because most Orthos come from Kenya, and are about 140MILLION years old at LEAST, they're nice and impacted, like smooth granite, and unlikely to release chemicals.