i have a 120 gallon tank 50lbs rock and a few fish. the other day some of my rock fell down and i kinda mix every thing up when i fix it so it was looking really ditying but it still looks dirty kinda a green clody look i dont understand what it is i did a 20 gallon water chang last night and it help but not much i test my water and every thing is fine. i have not got a skimmet yet could that be the problem and its been like this for about 5 days now