He means that a sand bed of sufficient depth (like yours is) and LR
will provide enough surface area to house more nitrifying bacteria than you will ever need. The addition of additional bio media will not help but hinder the DSB
's (deep sand bed) and LR
's ability to denitrify, leading to a build up of nitrate. Mechanical filtration (sponge, floss, etc.) will remove zooplankton and 'pods
from the water column and will trap detritus rather than allowing it to fall to the bottom where it can be processed into harmless material by the fauna of the sand bed.
Side note: if you don't have an abundance of said fauna, you need to get some and keep it fed so they multiply. The few pieces of LR
you have may not have enough worms to form a "seed" population in your DSB
. "Feed" your tank some flake or frozen food every few days to give the micro critters something to eat and they will multiply for you. If you don't see worm trails in your sand by the end of the month (or two), consider getting a detrivore kit to suppliment the sand fauna.
Good luck, it looks great so far!