It must have been an aluminium heatsink.
The Indium in Liquid metal will eat through aluminium. Only copper or nickel plated heatsinks can be used with liquid metal. It says so on the packet, at least my pack of Thermal Grizzly Conductonaut does.
I will try to add all the old tank's shrimps at the end of August to the new tank, had a problem with my chiller this morning, try to make it more efficient by adding a better heat sink grease, I added a liquid metal grease, apparently you can't add liquid metal, when heating up, the heat sink turning to dust, along with part of the cooler inlet and outlet.
So far the shrimps are ok.