Are the bubblers (what exactly do you mean by that? photo?) sitting directly on the bottom, or do they have some barrier (like Cecil's classic inverted garbage can lid) to keep them out of the sediment?

Tannic water often holds plenty of fish with no problems. AS you noted, one dead bass could have been frm anything.

"Live like you'll die tomorrow, but manage your grass like you'll live forever."
-S. M. Stirling
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