Check your lid. My guess is that you have pin hole light leaks. Usually they are found around the hole cut for the net cup. The water is foamy on top, the inside of the bucket and any hoses are slimy feeling and the roots have a slick feeling not to mention brown color. Odd's are your not using anything exotic in the water to change the root color so it' good old fashion root rot. Change the water, hose off the roots, use tap water to clean out the inside, the chlorine will help, and finally get a new lid or resolve the light leaks. Verify your air pump is sufficient for your reservoir, I'm guessing 60 GPH per 5 gallon bucket.