"Hmm, I'm thirsty" ..... DBW reaches over to a bucket of water and sticks his hand in to have a drink ....
Seriously though, for the direct absorbtion of anything to occur then there has to be the mechanism in place for that to happen. If it isn't then you can do what you like, add what you like etc, but it just wont happen.
For such a mechanism to be present then it has to be used in some manner, otherwise it would not be there. How much sugar, or any associated sugar, would be present in any significant amounts in water being flushed over a natural reef for a coral to be bothered utilising such a mechanism? Bacteria are far more superior at using any such thing, so before something like a coral would have a chance to get any access to sugar it would have been consumed by bacteria.
You have to also consider, where would such a source of sugar come from naturally anyway?
As to adding it to a reef tank, it is unlikely to cause any problems. Bacteria will just have a feast on it, that is all. More bacteria equals more food for organisms that prey on bacteria. You can achieve exactly the same thing by simply feeding the system more, and you are providing a more natural food source anyway.
When I first saw this subject I thought it was the feed the sand bed sugar type of things that was around a couple of years ago. That is also bit of a waste of time, unless carbon is the limiting nutrient in sand beds which is not the case I believe.
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