Hi Q we specialize in coralline algae spores for labs, universities, private and public aquariums and seeding artificial coral reefs offshore so I thought we could chime in. We study hundreds of different non articulated coralline species. There are around 2,000. It depends much on the specific species on how long they can survive outside of water. Species in the genera Porolithon, Lithophyllum, and some species of Hydrolithon can stay out of the water for 6 hours and be ok. These are usually species adapted to intense lighting and have adapted over millions of years to be out of the water during low tides, species like in the genera of Sporolithon, and Mesophyllum will not be able to tolerate being out of the water for more then 20 mins and will get stressed and lose pigmentation after just 5-10 mins out of the water. With some exceptions such as Sporolithon phtchodes and some others that slough epithelial cells in sheets.
The short answer is any time you expose coralline algae to air you run the risk of killing it. For moving tanks we suggest to have a spray bottle or 2 of saltwater and have a buddy stay with the tank during the transfer to keep spraying the tank every 5 mins. Once the coralline is white it is dead, you can scrape the glass or not that won't make a difference on the regrowth. Coralline is VERY sensitive to abrupt changes in salinity also, more so then any other water parameter. You never want to make changes too quickly, adjusting only 0.001 ppt per day. Allowing your new salt mix to settle over night and then retesting it again before adding it to your tank will give the most accurate readings as to if you're truly matching the parameters to your aquarium. Coralline truly lives up to the saying, that only bad things happen quickly in the hobby. The coralline will grow again though, if you want to DM us your mailing address after your parameters stabilize, we'll ship you out a free bottle of our coralline algae spores to help get you back on track again. Hope this helps somewhat and all the best on your new tank :)
