can diatom be dark brown/almost black?

[fullmonti]

I have a two year old sps tank. I was trying couple sponges & some one told me a little silicate may help sponges grow. I checked it out, & I found this to be true but might also encourage diatom growth. So I dosed a little for couple weeks. Well I now have some chocolate brown dust like stuff that forms on the sand at night, it mostly goes away during the day just a little hangs on in dark corners. I have stopped dosing & doing extra water changes. Pretty sure it's diatom & should go away now, right?

[jonbry123]

Usually with diatom growth the opposite is true. Growth is more evident with lights on then off. It is a form of micro algae utilizing light for photosynthesis.