How high can corals go

Funny I never thought to ask, but I see quite a few tanks with hard and/or soft corals rise up almost to the water line. I have been afraid to allow this to happen and consequently I only have my corals and rock piled up to about ¾ of the way. This way during my routine water changes they are never exposed to the air (I do a 20% change every 2 weeks). For all practical purposes this is fine but I just moved my leather down a bit and the acropora is soon to be exposed. Will my corals be harmed if they are exposed during water changes, were talking 20 minutes at most? Conspicuously, I don’t have any coralline algae growing on the back glass above this water line and this may be an answer in itself but I need experienced advice. Thanks

 

If you think about it there's alot of coral that get exposed to open air for hours at a time during low tide. I have a candy cane an inch or so below the water line that gets exposed every w/c and it's one of my better growing corals.

 

A brief exposure (5-10 min) to the air should be fine but place a soak towel or sponge if you have MH or fan blowing to prevent drying.

 

There are certain corals like seafans that need to stay under water. When you buy the coral from a reputable store ask the employee what is best for the coral. I usually pull the coral out of the bag and put it in the tank but some corals don't take well to that and those I let in directly with the bag submerged.

Yes there are corals that get exposed for hours during low tide but there are some deep water corals and those are the ones to be aware of. IMO

I do the same thing you do with the rocks only 2/3 the way up. I have my 40% water change (80 gal) delivered from a guy who gets the water from the ocean here in South Florida. A lot of my corals immediately spark to life when he does it. He charges about a dollar a gallon which works for me and saves me the time and energy and expense.

 

I have SPS, LPS, Zoo's and a few leathers that have grown to the point that they are almost completely out of the water during a normal water change and haven't experienced any problems.

 

Thanks for all the info, I felt some would be safe but it would be a terrible gamble. At least I know that some can and some can't so I'll research a bit more on my specific corals and perhaps rearrange them (again) in a manner that can accommodate if need be. A buck a gallon Marlinman? - you never need to mix salt? - think he'd deliver to Canada lol?
thanks again