I've recently lost both a royal gramma and a clown goby in my 30gal fowlr tank. The tank has been running for 6 months, I top off and make water changes with RO water regularly, no skimmer yet, but I am running filtration rated for 80 gallons. The only thing I've changed recently is adding a new mech filter. The fish seem fine one day and are dying the next... I don't know if this is a s@#& happens scenario or if something is legitimately wrong.

