In the 80s, I had 9 tanks (both fw & sw), totaling 500+ gallons in my parents' laundry room. No mold or fungus, but the clothes didn't seem to dry very fast in there
I now have 5 tanks (5g to 100g) in a small basement suite with similar results. However, I do have rust forming on the baseboard heaters, but no mold or fungus.
JME
Anthony