
I caught that to! LOL
%100 RTC, Definetly stress related but still completly normal in a barebottom tank... I noticed that they will get darker colors when the bottom of their tank has something on it (Prob trying to blend in abit)
Mine will also get very dark when he's being agressive (Sometimes likes to show the TSN who is boss)
Looks to me like your already at the point of needing to put that TSN in the pond but it could just be the angle that the pic was taken from (It appears that it's almost as long as that tank is deep)