This morning I noticed that my part of my zebra danios tail was missing she is very fat,and she is one of the three zebra danios and I have 4 neon tetras and 1 betta I noticed that the zebra danios always chase around eachother,and my betta has been having some issues with his tail too,and my neon tetras tail was missing before but its now healed. i know I deffinently have a nipper now the zebra danios are crazy they swim like mad men so should I add some plants in the tank to reduce the stress?