Who Gives A Fish Forums

I had the same issue last month. Turns out my tap water had traces of ammonia. Try testing your tap water first to rule that out. If it's clean, then it's probably something in the tank, like overfeeding or a dirty filter.

Your tank sounds like it's coming along nicely. How's the Rotala doing since you started cutting back on feeding?

Your setup sounds solid. I've had trouble with Rotala in the past, but keeping nitrates low seems to be the key. What's your filter setup like?