Hi there. I have a 55 gallon tank that gets some partial sunlight. I've recently added a second filter (both are 300 GPH, so between the two of them I'm finally circulating over 10 x my tank volume per hour), and I have a large air wand, so the circulation has definitely improved within the last couple weeks. This makes me think that the problem may go away over time once the oxygen level goes up. Anyway, I have brown spot algae diatoms on the two walls of the aquarium that get sunlight and on a large decoration. For the time being, I can keep up with them by scraping them off during water changes, but I'm concerned about whether or not they are bad for my fish. I have 2 comet goldfish in that tank. Is there a better method than scraping? I think soon it will be to the point where I'll have to scrape just about every day. I read the links in some of the other threads about causes of algae buildup and how to combat it as well as types of algae. One said that brown spot diatoms usually grow in tanks without much light, but I'm finding the opposite to be true. The side of the tank that doesn't get much light is totally fine. BTW, the water is completely clear, so there's no kind of "bloom" in the water... just brown spots on the sides. After reading the articles I'm trying to address all of the potential causes, but I'm wondering if there's a better fix than scraping and more importantly whether or not brown spot is harmful to fish. Thank you!