Methylene Blue, you know what that is correct ? Put a std does in some FW and then pump the water through GAC to see how much, how fast/long it takes the water clear. You could just do it in a bucket and set the bag in there with an aristone. This will give you a good idea after you done this a few times when to change it out. I'll bet you take out the GAC you are chucking the MB will be gone in a few hrs. and the water clear.