not big enough refugium

I have a 300 litre main tank with about 8 litre hang on back refugium with cheato and live sand in.Over the past 2 weeks my nitrate has gone down to about 10ppm and my phospate to about 0.25ppm.the cheato is now filling the refuge but i trim it every few days so it doesnt block the refuge,the fuge light is running on a reverse cycle to the main tank.Will my nitrate and phosphate ever got to 0 on such a small refugium?I only use ro water with the water changes.

 

Hard to say. It will depend on your cleaning, feeding and stocking. Too much of the last two and most likely not. Getting to 0 for NO3 and PO4 is not good for your corals. Aim for around 2 or 3 for NO3 and around .05 for PO4.