Will the diatoms go away (be replaced with other colored algae)? The brown mat over the glass is not very attractive

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Ahh, I've heard of the T5HO light. However, if I were to use any other type of light setup, I would need to retrofit my hood and I'm not good at stuff like that.
For the coral, I plan to just grow a few red or blue mushrooms. I read they don't need much light and I guess my one bulb will do fine if I put them at the top of the tank. Of course, I'll feed them too.