Really like the look of your iwagumi edge tank (http://sphotos.ak.fbcdn.net/hphotos-ak-ash2/hs477.ash2/75092_149205841790690_100001038261812_250713_2280825_n.jpg) and was wondering if you knew how much those three rocks weighed all together? also, whereabouts did you purchase them? i found a online retailer (http://www.aquaessentials.co.uk/mini-landscape-rock-per-kg-p-1437.html) and they guessed that the weight of your rocks would be 8kg.