finally went out and bought a 55 gallon (hood & lights), stand and filstar xp2 and im rather excited. anyways i have a couple of question i set it all up, filters workin and such, now my question can i add sand with the water already in as long as i turn off the filter? there arent any fish in it yet cause i have to cycle it before. and im thinking of gettin silica sand, so could i just add that right in the water? also, im thinking abuot getting a lotta river rock cause i want a rift lake (malawi) tank so should i use eggcrate (light diffuser) underneath the sand for extra support?