There was a thread on KP a while back where someone was asking about tiling the drip edge for their waterfall...i told them that unless you have a solid substrate (concrete) to bond to, the stone and mortar would just crack up...if you don't mortar it in then you get mulm and lots of other funk under the stone and that gives off the rotten egg sulfur aroma of death, which, as you are fully aware, is bad for our fish...I am a firm believer in a mud bottom or a liner system...I will never do rocks in my bottoms again...there are certain mortars that are waterproof but a brutha would go broke on the install.....LOL.....btw i started 50 yellow corn plants today which will go in the ground,..about 90-100 beans, peas and okra, and 4 cherry tomatoes and 4 goliaths, 4 red beauty bells and 4 golden bells too...they are all in those plastic net pots in clay/grow mix in plastic flat containers...they will sit in the square containers in a small amount of water to germinate and to acclimate to living in the water of the a/p system....