Onyx Substrate??

[500809052]

Has anyone tried Onyx Substrate before?? Just curious...
Naturally sourced fracted substrate for both saltwater and freshwater aquaria. Onyx Sand™ is exceptionally concentrated in iron and supply other important nutrients such as magnesium and manganese. Gravel modifiers such as laterite are therefore not necessary. Though very effective for freshwater planted aquaria, Onyx Sand™ is useful in all aquarium applications
including saltwater, reef, or African cichlid aquaria. Additionally, Onyx Sand™ provides a slight buffering capability that works to stabilize pH for the long term success of any aquatic environment.

 

[500809052]

i currently have play sand in both display and refug but i'm about to move to a new tank and was thinking of giving this onyx a shot....

 

[ophiura]

Anything that is "Concentrated in iron" is not something I would use in a reef tank, personally. Additionally it is described as basically being "best suited for a planted freshwater tank" and is commonly used in that application. This is another indication to me that it should not be used in a reef tank. I think it would be too nutrient rich, in addition to not being realistic (a black clay substrate). It is said that it can be used in place of laterite...again a substrate for planted tanks.
Basically, I would definitely never use it, personally, in a reef tank (or any saltwater tank to be honest). I would stick with play sand, which is far more natural for such a tank.
If it is black sand that you are looking for, there are other options. This is not one, IMO.