Any more room in my 46gal for one more thing?

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So im pretty sure I know the answer to this already but I figured it couldnt hurt to just throw this out as I havent done anything yet. So im getting my phosphates close to nil but still have a some different and interesting little algae growing about my reef. Was wondering if there was something to get that will graze on anything that pops up. All I have right now is carnivores basically and was thinking some diversity would be nice. My tank consists of a 46gal with 1 bengaii cardinal, 1 firefish, 1 longnose hawkfish and 1 six line wrasse. Oh and a tiger tail cucumber. (couple shrimps but im trapping them as soon as the trap arrives.) Im totally ok if im already at my limit. I kind of figured that I am but not really sure what I can get away with as im still pretty new. Thanks for any opinions.