what should my next piece of equipment be?

I believe Trent was referring to the possibility of Phosphates leaching back after sandbed disruption, or liverock saturation.

 

Ahhh. Got it

 

If you are thinking about getting a reactor for carbon i would consider a dual reactor from brs, once chamber for carbon, one chamber for GFO.

Later on down the road you might decide you want carbon and gfo and kick yourself for not spending the extra couple of bucks.

 

Zero phosphates aren't good in a reef tank because it causes problems with the exoskeleton so that's why it is suggested to be as low as .01-.02 up to .1 ppm.