I have a 20 tall and a thirty long. water is tap and is hard and ph range is on the high side (8-8.2) would like to do one of the shellie's and then apisto in the other. (currently have a (viking-kills everything) auratus who lives alone- and 4 venustus who are about 6 weeks. in other tanks) The question is about how many shellies in the 30 long to generate a duel colony one on each end, which shellie is best suited for this. Also in the 20 tall which apisto> knowing the ph might have to be worked on < has the most potential in this size tank. am continuing research, but as always there is conflicting ideas on line, experience speaks volumes. thanks