[Penguin]

My sister-in-law told me she's been having a problem with "cloudy water" and high ammonia readings in her tank the past couple of weeks. I was pretty surprised when I finally saw the tank yesterday, the water is very green, almost opaque. She says she's been doing large water changes but they haven't really helped. I recommended she leave the lights off for a few days, continue changing water, and maybe cut back on feedings. Any idea what's going on here, or suggestions? I haven't had a FW tank in a while.

Tank is a 27g, I believe; Whisper filter; river rock-like substrate; 2 small goldfish, 2 tri-color sharks (~3 in), 4 or 5 tiger barbs, and 2 other small fish (<2 in) that I'm not sure what they were.

TIA