If you had the newt for that long, seems to be working. I've seen this species in the wild and know a little about their Natural History. I have also kept them as well. I have found they do well in aquariums that are well planted with areas of land to crawl out on (cork bark/drift wood etc.) They do not like heavy filtration and can get stressed out with strong filters or overcrowding. They do cohabitate with various frog species larva (southern lepord frog, sping peeper to name a few). Their ponds are located in dense pine forrests on the coastal plains of North/South Carolina. These ponds are stagnant and sometimes dry up to a mud bogg in drought years. No fish species are in these ponds and may add stress to this species while in captivity. I would nix the minnow and keep the tadpoles to a minimum. I'm a purest when it comes to keeping newts and do not mix them at all. You always run the risk of stressing them out or passing parisites/disease to your pet. Your newt may be healthy now, but if one of his tank mates gets diseased (fish or tadpole), the newt will only be suceptable as well.