[alexandrie]

My idea is that a good carbon source will increase phosphate consumption by xootanthellas thus increasing coral growth and reducing phosphate levels in water.this may explain how vitamin c works.

I think it is all a problem of equilibrium between Carbon, Nitrogen and Phosphate proportion.
too low nitrogen will lead to bad Phosphate consumption by cells

Too much phosphate is as harmful as zero phosphate etc..

I can t deny the utility of vitamin c in the treatment of melting zoa syndrome.
But we don t have the full explanation of its mechanism of action.