I have a 90 gl Tang tank, previously kept Malawi. I used alot of Lace rock. It is attractive but all the crevices in the surface hold alot of sediment and debris. I have stated weeding it out and replacing it with Texas holly rock. Interesting rock with numerous holes and tunnels. It also has a haed smooth surface. Another thing that i have experienced with Lace rock is that it becomes pretty brittle after a long period....... I also have a very large piece of Floida field stone, a type of lime rock, helps with the ph with no problems,,,, 2 years in the tank, now.