in a SW tank it is very, very important to siphon out detritus tha accumulates on the bottom of the tank. it is usually a grey fluffy stuff that will go water born with the slightest brush of water in the area. unfortunately is that the detritus tends to accumulate in the hardest to reach areas of the tank. depending on your substrate siphoning detritus can be troublesome.
if detritus is left to sit it will leach its phosphates into the SB. these phosphates can then work their way up through the LR. this will lead to hair algae and cyano problems.
i do 15g water changes every week. i have extreme flow so i get very little detritus in the tank itseld. i do however get it in the sump. i siphon it out of the sump during the WC. what i mean be extreme flow is 7000gph in a 125g tank.
G~