This has worked for me pretty well. I use it maybe once or twice a year when things get out of hand. Many years ago, a veterinary office in Germany tested it and found that this is actually erythromycin sulfate, an antibiotic, although Boyd Enterprises claims it is not.... So keep that in mind.Chemiclean - Chemi-pure Advanced Aquarist Products
chemi-pure.com
They are supposed to work great and are recommended often to help finish off the dreaded cyano. I bought a small pack of each for stock to test.