Listen I'm not backing ecotech because that is some crap the large amount of failures and knowing mine will probably break... however I do have to point out an array of items that's leads me to believe this may be other sources of contamination "if" the tin caused the death. 1. I can't imagine any tin is utilized on the wetside. The magnet is more the likely a ferrous type magnet (iron) . With a plastic covering on it I doubt tin plating would be utilized. The extra expenses would not be worth the un added benefit it would "produce". Tin plating may be utilized on the propellor shaft but more than likely it a cheap 304 or 308 stainless steel consisting mainly of iron carbon and chromium. In the event tin was utilized the brown corrosion shown in the pictures are not tin corrosion that is more then likely ferrous oxide (rust) tin doesn't corrode in seawater as it only corrodes in highly alkaline situations (higher than our tank ph unless u for some reason keep it at 12) . Than we go to toxicity of marine animals with excess trace minerals and studies pertaining...
In almost all studies while arsenic lead vanadium and potassium have been in excess levels toxicity has presented itself however even when sn(tin) levels have been elevated due to pulltion toxicity hasn't been present until .1mg/l- 2.1mg/ml which is like ten times less than that of ur levels so although I think ecotech should start a recall on these maybe look elsewhere for ur tin concentrations and investable poisoning