Professor Amos 25oz Fast Toilet & Tank Concentrate FAST Toilet & Tank cleaner is a thick, concentrated formula that was developed to dissolve lime scale, rust, mold and mildew stains found in toilets. The color-changing solution goes on green and changes to blue as it works. It clings to surfaces allowing for longer contact time so the active ingredients can do the work instead of hard elbow grease. What You Get 25 oz. bottle of Professor Amos FAST Toilet & Tank Concentrate