Ive had aquariums all my life.about 50 years.I have a 55 gal aquarium.we cleaned it out about a month ago a total clean.Then one day i walked in the room it smelled of a dirty dog,I did just get a puppy,I thought is she pooping in here,it just smelled like a dirty dog,I washed the rug.Later when I lifted the lid on aquar.I smelled it alot,its the tank.Then a few days later everything turned dark brown,stones,plants.does anyone know whats going on,Ive never seen this in all the years Ive had fish.