I have no water pollution to speak of. I just replaced my treatment plant so thats not an issue. I know that 6 tiles apart too close, but I kept building my pipes closer and closer to together and I kept getting brown spots all over. It may be the age of my pumps. I have three now. I had two large pumps and like four small, but I replaced the four small ones with one large. I guess I could replaced the orginal two large pumps, but I dont think they are that old.