never had mine crack and i didnt use the big crack filler. I even used it for the bottom, just stuck basketts and am using wandering plants that do not use much subtrate, such as resurection ferns, wandering jews(wierd name but thats the locality of the plant, it is realy hardy and spreads everywhere), spider plants, etc. Looks great to, I just laid them in there and they grew like crazy,
Silicone is what i used, cant be used below the water level it will cause the coco fiber to come off(this happened to me on some parts) and it is probally the quickest way to get the job done. Another way is the Concrete primer method, and teh weld bond method. Not too familiar with those though they take a week to dry though thats the negetive part of it.
Ryan