No kent carbon was used.

I'd investigate other sources, a brass fitting won't just dissolve in fresh water to the point it would become toxic.

Have you tested the fresh water in the top off container for copper? If this is the source the level of copper should be noticeably higher than what's in the tank.

Do you use RO water? If you do, its not good.......
Do not run RO with copper or brass products, it will pit the piping very quickly and you'll have contamination.

The container is also used for mixing water for water changes and yes it has been confirmed as the source. From a long night of internet reading the use of DI resin to filter the water will greatly accelerate the breakdown of the metals and it can only take a few hours to become toxic.

Ya i use ro/di system for filtering and that seems to be what really makes a copper fitting worse.

Interesting... note to self no metallic fittings on RO lines.

Best of luck with the recovery. I'm sure a series of significant water changes will reduce the contamination to below toxic levels.

Yep, because of the pH of the RO, it will pit very quickly.
We run into this problem quite often in the trade.

It doesn't take very much time to reach toxic levels so a big part of this topic prevention for others. A small simple fitting that most would never think twice about can wipe out an entire system at a very rapid rate. I will try and get a pic of what the fitting looks like up later on.

That's sad. I had copper poisoning from Kent carbon and a lot of my corals died. After many water changes I had my water tested by a pro lab and it was free of copper so I guess my liverock did not absorb too much. My corals did absorb some copper because many of my remaining SPS are now fragile and bristle and they break at the slightest touch.

I used Polyfilter to help remove the copper with water changes. I would also use cuprisorb if I were you. Everything that is still alive in my tank is slowly recovering. It really does not take a large amount of free copper to kill corals.

I have a brass fitting on my ato as well. I'm heading home to get it the hell out of my water. Thanks for the post.