Man this is one of those lores isn’t it. I don’t know the answer but this topic sure sits right on top of the galvanized fence.doesnt it? Either “dead fish for sure” or “I’ve been keeping fish for 25 years in galvi tubs”. Treated, sealed, not sealed....I like to call these “thorns” of knowledge. We all know most of them. Boils down to personal experience doesn’t it? I mean some of the folks here are literally walking aquatic encyclopedias who’s knowledge far surpasses many of us put together. Science is science. It does not deceive but it has been wrong. Bottom line, I came here not having a clue how to create and maintain a non-closed mini ecosystem. The knowledge and wisdom combined I have gained would fill a book. My pond has been running 60+ days. I started in March.