The great sand bed debate. I love this one. Run as many experiments as you want and apply the biological and chemistry theory as you see fit. In the end "what works for one may not for another." There are just too many factors involved in a closed system to say what "one" method is the best. Light cycle, temp, Ph, alk, etc, etc ....all are factors that apply to bacterial lag, expotential, and stationary phases.

Nitrate at 25ppm means your biological filtration is working.Could it be better, sure. If your system shows no adverse effects at that level...your good.