So I have a fully cycled 20 gallon tank setup for almost 2 years, but recently every time I buy fish I loss a majority of them within a week. Example: I bought 6 panda Corys and 4 otos, 3 days after purchasing them 1 oto and two pandas died now 10 days after 2 more pandas died. Should I be doing a salt quarantine to avoid these losses?