I wouldn't worry about dosing a tank that small, just do weekly water changes 3-5 gallons. that's all i did when I had my biocubes, also look into better lights. how big are your temp swings from its lowest at night till hottest when lights on.

I dose my current tank because I have a high demand for calcium with all the sps I have, also because nutrients are used up quickly and it would be too much trouble to change 30g a week.