my poor Betta

My poor Betta...I got 4 ghost shrimp to help with the cleanliness of the bottom of my Betta's 5 gallon tank...at first I was nervous that Harry (my Betta) would eat the shrimp, he did chase them a little, but then last night when I went to feed him a few pellets, one of the ghost shrimp swam up and grabbed hold of his tail...it took a few seconds for Harry to shake it off, upon closer inspection it looks like Harry's tail has been chewed up on the end. I was horrified, needless to say the ghost shrimp were removed...I was just wondering if I need to be proactive and medicate the tank to prevent fin rot since I have been reading that it is real hard to treat. Poor Harry I feel so bad, that I did something to cause him harm. I'd hate for him to get sick. I keep his water real clean. Any advice out there?

Those little invertebrates are skilled predators, and male Bettas are slow swimmers. If you keep the aquarium clean with weekly partial water changes, Harry should get better on his own. Medications can have wide ranging effects, so they are better used as a last resort.