Tail tears are common and they will heal on their own but the Melafix may speed up the process.
My bottle of Melafix has on it; Contains Melaleuca CAS#8008-98-8 and inert ingredients.
When I looked up the Melaleuca bit I found this. Once on that page, click on the Risk Satements! Interestingly, apart from the carcinogens (plus lots of sentences starting with 'harmful, toxic, or very toxic), it also says Very Toxic to aquatic organisms, Toxic to aquatic organisms, Harmful to aquatic organisms, May cause long-term adverse effects in the aquatic environment, Toxic to flora, Toxic to fauna. :-?
My bottle also says; Warning. This product contains a chemical known to the State of California to cause cancer or birth defects or other reproductive harm.