I had BGA, finally... *Sigh*...

BUT, it is in my vivarium tank...



The water temperature in the vivarium is high... It should be about 32-33C, which is what I will see when I check before I switch off the lights. The water is shallow and the tank is lit by 3 x 24W T5HO. Water movement is limited as the water fall flow is hampered by the thick plant growth...

I would like to understand, why did the BGS appear suddenly, after almost half a year? And how to get rid of it? (This is a vivarium) It now had slowly began to other areas...