That so called mask appears in my fish every night , in this tank (190g) i have only two PB´s and a LMB the three of them are about 3-4", so i don´t think they are harassed by the LMB it appears to be the other way around, when it comes to feeding they fight like maniacs for a piece of frozen shrimp and most of the times the PB´s win.
i do a 50% water change every week, water parameters are good (here in my city Monterrey we have high ph water so it`s kind of hard to keep it low, ph is about 7.8).
The good thing here i think is that hey are eating very good and they don`t seem ill in any way.
I can´t upload another picture cause my camera is not working
Thank you guys for all the help
Greetings from Mexico
Carlos