To start with I'd be doing weekly water changes (5% - 10%) siphoning off as much algae as I can. Steel Straws may help maximise reducing the unwantd stuff without going over 20% - 40% monthly total and sand can be rinsed off in fresh nwater or aquarium water and returned. Nuisance algae can dump a lot of DOC into water that promotes microbial issues with corals and you don't have a lot of corals yet to counter by promoting microbial beneficial processes. As far as "ideal" above .03 mg/l, this was the threshold number identfied by researchers at Southampton University to reduce the risk of phosphorus deficiency. For refference, upwelling will expose corals to .3 mg/l, one study showed increased growth in Acropora murcata at .5 mg/l, RIchard Ross (Thales on the forums) has sexually reproduced acropora millipora at .9 mg/l.