I just got a betta fish from the fish store for six dollars yesterday and this is my first time keeping a betta.. I have a six gallon cycled tank with a heater (currently at 78f) with 4 amano shrimp that were already in there before i got the betta. I just noticed a slight tear in his tail... i cant really remember if the tear was already there at the fish store, or if this is something new. Is this fin rot??? And if so will clean water at a nice temperature (78f) be enough to naturally cure him?? I really dont like dosing the tank with anything. Please help!!!! Oh and when i got the betta, he was in a tiny cup and the water was almost lime green... the pet store guy swore it was because of almond leaves but i think it may have been really really bad quality water. Could that have made my betta sick?