[ccp4bb] Unidentified density.

[<Justyna Wojdyla>]

I have MES, Tris, maleic acid and small PEG in my solution. No  
reducing agents and no cryo (and no salt or EDTA). Calcium seems to be  
the best fit (assuming 100 percent occupancy) and also literature  
suggests it. I tried Ni and Mn but they give negative density after  
refinement.
Thank you all for your suggestions.
Justyna