My 55 Gal has been up and running for about three years now, I recently changed my rocks around and added some new sand, that was about 2 months ago and ever since i cant keep the reddish brown algae off my sand and a few select pieces of rock. My yellow tang eats some of it as well at my coral beauty but i need some advice. I've been doing 10 to 14 gallon changes every two to three weeks. my light cycle hasnt changed I have them on only about 6 hours a day. there is one more thing im concerned about and that is i change my filter material in the sump once every other pwc but the spongy like material that sits at the bottom hasnt been changed like probably 10 months or so should i be replacing with me other filter materials? im just trying to narrow down why the algae isnt going away. my waters been testing vigorously and everything checks out. it's so strange. i dont have any corals could i use some kind of algae control drops or something help!