Folks, if you've recently upgraded or renewed your annual club membership but it's still not active, please reach out to the BOD or a moderator. The PayPal system has a slight bug which it doesn't allow it to activate the account on it's own.
When in the original tank, were they always close or did the 3rd hang around away from the pair? It's likely that they got aggressive because of the lack of space.
They will go for shrimp 100%, not snails, unsure about other inverts. It does show interest in guppies ( or other tiny fish), but unsure if it's just curious or looking to eat them, usually the other fish will get to them before it tries. They are very hardy fish, after you get it to eat...
Reduce the lighting and try reverse schedule from you main light. Is the chaeto growing well with 24h lighting or is it starting to bleach out? Eventually you'll figure out the balance of light to keep up with your filtration demand.