Life is making posting difficult but this should start me off again.

Lucia, the Mermaid Princess of the North Pacific Ocean, saved a boy seven years prior to the story from a deadly tsunami, entrusting him with her Pink Pearl. Present day and Lucia tracks down the boy she loves, a surfer named Kaito but unable to tell him the truth, Lucia must try and help him remember. Meanwhile water demons attack the Sea Worlds, so it's up to Lucia and her friends to gather the remaining mermaid princesses to summon Sea Goddess Aqua Regina to save the Kingdom. They do so by transforming into idols and singing away the evil.
Back in the past, this was a guilty pleasure, it's a novelty to watch these girls perform which gets better when going up against singing villains, in fact the villain songs made my car playlist. But now, it's worst than I remember.
There's only so much of the same set pieces I can stand, the series is notoriously long and can be an absolute slog to sit through, there's nothing particularly wrong with much else, the character arcs are well written along with the characters themselves being very joyful; the Orange Mermaid Princess especially noteworthy for her performance. It's just too long.
It was meant to have a dub and it is finished just never released, the network still has the footage locked up.
There is one dub that does make the series so much better and that's the Italian dub version. Italy have a good record for shojo series and they gave Mermaid Melody some much needed justice.
Final Verdict: it's fine but way too long for a series that has too many set pieces, could easily shorten to 26 episodes from it's 91. Italian dub does improve the show.