Great looking tank Kiriyama.
Just about to start a 300l tangs tank myself but two things held me back. First was which substrate to put in. Wasn't sure how black would look but after seeing your tank I'm now sold so black it is. Will be adding a mixture of 1mm and 2mm black quartz.
Only prob I have now is that I have a pair of breeding convicts in my 300ltr tank at the moment and the female's just given birth to a brood...looks like the tangs project might have to wait for another month or so
Cheers
have a look on warehouse aquatics, they have fine grade black sand, heard a lot about quartz, have heard it has sharp edges

, not so good for shell dwellers
I still have a reflector for the main tube in the 190ltr, going for some paracyps once the trops are moved from the 240, cyps will be moved into the 240 along with kungweensis and a pair of dwarf comps, oh oh and hopefully getting some caudopunctatus to add to the mix

. 190 will hold xenos, paracyps and a pair of dwarf comps
Good luck when you set up your tang tank, they are real interesting