8. If an anoxic sand bed needs to be removed from a reef aquarium thatcontains organisms that cannot be relocated out of harm's way, the following precautions may be useful based on the principles detailed in previous sections, although I've not tested any to see how effective they are:
A. Remove delicate organisms from the tank system, if possible.
B. Perform the change when the lights are as bright as possible, preferably near the end of the light cycle. The lights drive the O<sub>2</sub> concentration higher, speeding the oxidative removal of hydrogen sulfide, and the light itself catalyzes the oxidation of H<sub>2</sub>S.
C. Maximize aeration. A high oxygen level drives hydrogen sulfide oxidation, and high aeration drives some H<sub>2</sub>S off as volatile H<sub>2</sub>S gas.
D. Add an iron supplement to help catalyze the oxidation of hydrogen sulfide and the precipitation of ferrous and/or ferric sulfide. Use one that's chelated to an organic; either ferrous or ferric iron works fine.
E. Pass the water over iron oxide/hydroxide (GFO) to convert hydrogen sulfide to elemental sulfur.
F. Pass the water over activated carbon, which may bind some sulfide and may also catalyze the oxidation. If forced to choose between carbon and GFO, I'd pick the GFO media.
