Algae Invasion!!!!

[Leelu95]

I have a 55gl tank. Within a week of doing water changes the WHOLE tank turns completely green! I have a double filter and 2 Plecos... And i'm not sure whats going on.
The population in my tank are as follows....
2 Black fin Tetras
2 Tiger Barbs.
2 Giant Danios.
2 Blue Gourami.
2 Plecos.
2 Pictus Catfish.