Has anyone ever used Featherock for base rock?

[Reef_kid]

this feather rock is great for landscarping but the problem with it is that it is so light and porouse that it floats!!
i have used it for landscaping.. and thought about using it as base rock
althought because it is volcanic rock it may release many toxins into the water and the fact that it floats !!!
so it is better to go with the real thing !!
you can get tufa from some places for very cheep but you have to phone around!!
cheers
dave