Mako Mermaids - Season 2+3

Two new mermaids arrive and are afraid that Zac is a threat to mermaid pods, but they don't realize that there is another mermaid in addition to Zac in town bent on seizing Mako Island for himself. The mystery of Mako deepens, when Zac discovers the ruins of an ancient Merman Chamber. The entrance to it opens up on a full moon, just like with the Trident Chamber.