I was an industry rep for a long time..... .25 PO is amazing! I have used EM several times over the last 15 years or so and if used properly, no problem. Just be sure you are not just curing the symptom, when you should be curing the cause. In other words, if your water perameters are good, you have a skimmer and are doing things as you should, use EM, get rid of the slime and it won't come back....Turn off your skimmer and suspend carbon/phosban if you use it. Sure, it is drastic but it works. Do a search and see what others think. I used to call on the best stores in W. New York and Canada and know many who have used EM w. no problem.