Try the ultimate sterotype predator, the Red Belly Piranha..............6-8 would do fine for life in the 150g...........Or, a FAjahaka Puffer for the 150g........................The 30g, a well planted tank............As easy it may seem to raise a well planted tank, it is not..........I have tried many times, and I have been doing the tropical fish hobby for more than 20 years.........Once you get the plants settled, try filling it with a dozen Dwarf Puffers...............Or, throw in a dozen Exodon fish..............