Last week I did a routine 20% water change in my 55 gallon tank, which contains a Blue Jaw Trigger (about 3 inches) and a Niger Trigger (about 2 inches). Over the past few days since then, all the algae in the tank has died off (it's unwanted hair/micro algae and hence unwanted). Also the water has turned cloudy. The fish seem to be behaving normally, but I am slightly concered that the algae die off could be a sign of some trouble to come. Anyone know anything about this? The tank has been up about 6 months and until now everything has been normal. Decorations include dried coral and rocks. No live rocks or anything like that. Filtration is provided by an Emperor 400 (400 gph) with an additional 100 gph of water movement provided by a powerhead. Temp has been constant at 80 degrees. Thanks for reading.