Serial killer fish in your tank...what triggers them?
I kind of wince when I hear the phrase 'showpiece fish'. Most tend to be of a pushy species, and if you don't give them enough room...your other fish start disappearing. They don't even have to be that huge a fish---if your tank size makes them feel cramped, they just start adjusting the aquarium population until they feel calmer in the traffic flow. Your other fish, in a healthy tank, just start not reporting for feeding. Sometimes you'll...

When and how to start with corals...
Corals are in a way a responsibility: their collection in the wild likely cannot continue unrestricted: there is already a call for certain ones not to be collected. Communities have taken to aquaculturing them---putting them in lagoons where they can be grown in native waters, rather like farming.

And we can grow them for domestic sale or trade. Certain ones are quite easy to grow and break apart for sale, and if you want to get into this,...

Do you need GFO: how to use it...RE PHOSPHATE AND ALGAE PLAGUE
Granulated Ferrous Oxide is, in effect, rusty iron pellets made porous, specifically to sop up and hold phosphate out of your water.

Rock, sand, and tapwater all contribute phosphate to your tank, and algae loves it...especially hair and film algae. Some rock is worse than others in this regard---but it can be some of the prettier rock. And 'new' rock goes through a period when it starts slowly 'leaking' phospate...