I have used white vinegar to clean mine and it does a good job. It won't work as good as bleach but the styrofoam will absorb bleach. Minnows and bleach don't work so well. just fill up your bucket to the scum line and let it sit for a while. Then dump the vinegar and rinse out the bucket a few times and then fill with water and let it sit for a while and rinse again. You won't totally get rid of the line but most of the bad stuff that would hurt the minnows will be gone. Hope this helps. CF