Make sure there is no fragrance or other additive .
The ingredients should be listed on box .
I agree no reason to treat for anything unless you have suspicions .
Well It says active ingredients of Magnesium sulphate (100%) for laxatives and Magnesium 9.8% and Sulphur 12.8% for fertilizer uses...Nothing extra is mentioned..
I have checked the ammonia just now. It's back to 0 ppm (Yellow on API kit, can't say if it is exactly 0) after doing the water changes. All fish are back again and swimming.