I have a FeCl3 tank that I use to dip spruce wood in. After 2–3 weeks a fungus appears in the tank and it keeps growing with time. The fungus has a white colour and is spread throughout the whole tank. It looks like mainly on the surface but its everywhere in the fluid. The FeCl3 solution has pH 1 and that doesn't change with time. Can anybody tell me what it might be? What's the best way to make sure it doesn't occur anymore?