HELP! Nitrate spike - things going down fast :(

[Jessie]

Ok, I have a 30g, 2 months old, cycled with used live rock and sand, fluval 306 (phosph & carbon & live rock). Salinity 1.025, pH 8.1, NH3 & NO2 are 0, NO3 is 15mg, PO4 0.1, Starry Blenny turned white & freaking out (now has 50% color back and is hiding), even clownfish went crazy! Hammer coral tucked up about 2hrs ago, and fuzzy green mushrooms are closing. Just got the Blenny and corals in the past 2 days...
Did a 10% water change - would have done more but that's all the RO water I had left...

Any home remedy available at 1am (besides water change) that can save this tank from biting the dust? If not, what would be the first thing I should do for the tank tomorrow? 50% water change?? What else besides Nitrate would do this.

Thanks in advance for any info, this saltwater reef keeping is more stressful than I had imagined