License to krill

Replacing Expelled Zooxanthellae


Supporting Member
Was talking a bit about coral bleaching in our big tank with my students and how it results from zooxanthellae being expelled. A student asked if we should add zooxanthellae like we add 2-part. A quick search revealed that there are free floating zooxanthellae in the ocean. I asked Chad at Reed Mariculture about it and he said AlgaGen cultures this and has a product:
I find this very interesting. Has anyone used this product or know about zooxanthellae in the water column? I had heard that corals may take in some from nearby or grafted corals which changes their coloration. I also heard that once zooxanthellae have been expelled, you cannot be sure the coral will color up again and it can stay brown. Now I am all curious about this topic.

A Aaron

Supporting Member
I think even when they are brown they still contain there full percentage of zooxanthellae. It’s when they actually bleach they have expelled it. Could be wrong.
I have a blasto that got very unhappy with a alk spike and it threw up all the green zooxanthellae in the center of it. I have had it for 6 months since then and it’s probably only regenerated 10% of what it should have. Sps will pretty much always die though from what I’ve seen in my tank. I do wonder if it would help putting it into the water.


Supporting Member
I wonder if the availability of zooxanthellae may have some connection with spawning. I mean the male and female parts are there but the coral can’t grow without zoox. Maybe that’s a missing component in our tanks. I have no source material to base this from, I’m just throwing it out there as a possibility.


Supporting Member
Funny. I was just about to post about the Phyco Pure stuff when i saw this thread so adding here.

I have a high end nem, Ultimate Chicago Sunburst, the bleached out due to my heater accidentally being unplugged and leaving my tank to freeze for about a month...there's no heat in my detached office.

So I ordered a bottle in efforts of trying to save it and restore the zooxanthellae since there's no other source of it (i.e., no other corals in the tank)

Just did my first dose... and will keep folks here posted.

Interestingly enough, the nem's mouth is stretched out and puckering right after i placed a direct dose of the liquid around its mouth. (Directions mentioned to add to high flow)



Supporting Member
Might be my imagination but my nem looks a tad richer in color today. Not the best 1:1 comparison since not in same pose but tentacles look deeper.

Same light and conditions.

Top shot, today. Other shot from last night


Staff member
I’ve always been curious how much of distinctive coloration is due to distinct zooxanthellae. It’s pretty obvious that they contribute a lot to coloration, since when corals lose them they turn white.


Supporting Member
Most coloration is actually contained within the tissue itself but the zooxanthallae fills in the translucency to make the color stand out. Think of like putting a black background to white text.

That said, the coloration does adapt with different lighting though...