I don't know if the cause is the same in my situation, but my bathroom is smelling like a dead fish. The toilet flushes and the drains flow just fine. I don't have a septic system. We live in the city. Would I do the same thing? Turn off the water and poor bleach in my toilet and such as you described above? Please advise. Thx

If you look at the bottom of thus page there are some 4-5 posts with this exact problem listed also,perhaps one of them can answer your question.

If not,looking for the source might be as simple as inside a cabinet under the p-trap,perhaps a broken pipe in the walls(looking around for evidence of water leeaking below the entire room,if possible),there are many places a bathroom can have smells(s=especially in the summer and winter months when most windows are closed)

Back to you.