White Patch on Blue Tang

Sulfur smell? Almost sounds like something bloomed and then died in there? Have you tested the water at all, like a baseline test or something? I too agree that you shouldn't use that water. Strange.
 
I'd not use any of the water that smelled like sulfur. What kind of holding tank is it?

It is the pressurized tank that goes with the RO/DI unit. The water only smells right after coming out of the tank. If it goes through the unit but not the tank it doesn't smell or if it sits for a day inside a plastic water jug (not air tight) it doesn't smell. I tested the water coming out of the tank and it is ammonia 0, nitrite 0. For reference my tap water is also 0/0/0.
 
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