Lugols is strong stuff! Years ago I got ahold of some lab grade KI (potassium iodide) and started adding it for some zenia I recently got. At first the zenia went crazy then after a month or so of regular dosing I woke up one morning to a nuked tank. I had apparently added enough to the point that it acted as an antimicrobial and killed my bio filter. There were no Iodine test kits at the time and I have since relied on water changes for Iodine replacement.