[Reefmack]

Hi Laurent. What test kits are you using, or are you using a strip test. The strips are notoriously inaccurate & if that's what you're using I'd get one of the solution tests. I'd hate to see you thinking that you have nitrites, and postponing a CUC, if you really don't have the nitrites.

I think a 50% water change would be a real pain - if it was me I'd just start smaller ones more frequently.

Are those "green spots" algae round and shiny? If yes it's probably bubble algae (vallonia - sp?). Can be a nuisance but I've always found the ones I had easy to remove - the shell is pretty tough. Some say if you break them they spread & other say that'a a bunch of BS. If I remember correctly emerald crabs may eat the small bubbles. That white "star" - hard to tell - might be a duster or one of those tiny asterina stars. Looks like too many legs for the star though.

The cured LR from my LFS looks like your piece. It'll darken up eventually & you may be pleasantly surprised by the life on it. I see a lot of little featherdusters. etc. on the white rock in my lfs's tank.