I believe tetracycline can be pretty hard on bettas and can potentially cause damage to the liver if used too long or at the wrong dosage.
I only use medication in case of serious infection or disease. Fin rot is generally treatable with high-protein foods and clean, heated water tinted with IAL like Bombalurina said above.
Unless you are very certain of what you are treating for, don't medicate. Using the wrong medication at the wrong time can lead to resistant strains of bacteria that are going to be near impossible to eradicate. Also medications can be hard on an already stressed fish, so it's always important to select the right one and dose it according to the instructions.
I only use medication in case of serious infection or disease. Fin rot is generally treatable with high-protein foods and clean, heated water tinted with IAL like Bombalurina said above.
Unless you are very certain of what you are treating for, don't medicate. Using the wrong medication at the wrong time can lead to resistant strains of bacteria that are going to be near impossible to eradicate. Also medications can be hard on an already stressed fish, so it's always important to select the right one and dose it according to the instructions.
