Danios attacking cardinal tetras
I have a 55gal tank currently stocked with the following fish:
4x Cardinal Tetras
5x Zebra Danios
3x Cory Cats
3x Red Dwarf Gouramis
The tetras were the latest addition last week (started with 6). Right after adding the tetras, the danios would just not leave them alone. The tetras found each other and had started schooling, but right away the danios split them up and started chasing them. The danios split into two groups and each group would harass a tetra for a while and then move on to another one. The next morning one tetra was dead against the filter intake (I can't find the second one that's missing - I've checked in all of my decorations and its not there).
After the first night, though, it seemed like they started leaving them alone, but this morning I noticed that the four remaining tetras all have damaged fins. I've kept many tanks with danios and tetras and I've never seen this behavior before. Honestly, I was more nervous about the dwarf gouramis, but I've only ever seen them chasing each other - they typically leave my other fish alone.
Water chemistry looks fine - no ammonia/nitrite, low levels of nitrate, and neutral pH.
Short of removing one group, is there anything I can do?