His words are very true. I've been arguing the same for years that iodine was never an issue. Some people just do not accept this fact. The additive that you really have to watched out for is yellow prussiate. It produces hydrogen cyanide when exposed to sunlight or any light with the same spectrum. It's toxic and can sicken or kill your fish.
However, I do not advise adding it on a regular basis. Add it only if it is necessary albeit the nitrite shot up and fish showed signs of nitrite intoxication or brown blood disease (a result of high nitrite) or the fish is showing signs of ich (parasites) and severe injuries. It helps keep the bacteria from latching on the wounds and heal wounds fast.
However, I do not advise adding it on a regular basis. Add it only if it is necessary albeit the nitrite shot up and fish showed signs of nitrite intoxication or brown blood disease (a result of high nitrite) or the fish is showing signs of ich (parasites) and severe injuries. It helps keep the bacteria from latching on the wounds and heal wounds fast.