I have white/opaque water storage tank that is about 16 gallons. It has started to accumulate brown algae, or perhaps (unlikely) mold/mildew. I have it near a small window that gets almost no light as it is near the north side of the house and hidden behind a huge bush. Is this a common issue, or is this literally a light thing. I guess maybe it is obvious, but should I try and filter out any or all light? It looks pretty bad, not sure if it has an effect on the water quality.