Strange tetra behavior
Hello, I'm fairly new to the aquarium world but I have done my fair share of research about all types of fish. I've had lots of guppies and have had no luck with them. Yesterday my last male turquoise guppy died and I cleaned out my tank and did the proper steps to get any bad bacteria out. I just added 5 new additions, Long finned black skirt tetra's. They seem to be doing great now but earlier they seemed to be acting a bit strange. 2 of them were not really swimming around very much and it appeared as if they were "shaking" but I'm not sure if they were really shaking. They were making really sharp movements in a single place. I'm not sure what's wrong with them if anything but it has got me a little worried because of my bad luck with my guppies. If anyone has any advice to give me I would greatly appreciate it. Thank you.