Tiger Barb Major Problems

[Barb738]

Hi, just recently my Tiger Barbs have been acting very strangely, whenever I turn on my tank light, they go insane, they dart around everywhere and there scales darken. I left the light on for a while to see if they would calm down, I figured maybe the light was dazzling them or something, however, now one of them have just died!
I really need some advice, what should I do? And whats happening to my fish?!

 

[WILDER]

Turning tanks light on can stress fish, and even more if there from the wild.
Need to look at your stats in ammonia,nitrite,nitrate, and ph.
How many gallons or litres is the tank.
And full stock list of fish how many and which type.