I don't want to minimize the situation WRT to your children's health (I have two of my own), but how could strep be caused from higher than normal humidity? Isn't it a viral infection? Really strange! Same with the lung infection your son has. I am no doctor but two infections being caused from humidity or possible air born viruses stemming from a fish tank. I would seek a second opionion before you tear your tank apart, IMO.
The only thing I can think is that the humidity is causing algae problems in your house
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