The picture doesn't do the horn justice-the details make it look like some kind of Victorian era debris from a shipwreck.
It demands a good try! I can imagine it emerging from the slope of the substrate, in a thicket of plants.
Today I completely disassembled, degreased and cleaned it. I will fill it with sand and seal it with aquarium silicone at every tuning slide, valve assy, etc. I'll seal and plug the bell in a bit, inside the shadow. This should cut exposure by ~40% which must be good a good thing. I put a 5g tank out in the breezeway where it gets light-we'll see how hot it gets. It may need more shade. I'll put some plants in and see that they're stable. If I can get the temp under control, I'll throw in a couple of Guppies. When it's clear things are stable, I'll drop in the horn and see what happens and how fast. In this small environment I'd expect if toxicity is a large issue, it would manifest quickly. I wish I could find an economical way to monitor the copper and zink chemistry. I'm wondering if weekly 33% water changes would keep it in the healthy zone in the 29g. At this point this is my (only) best plan. Any educated coaching is appreciated.