Ok, well first off this is a filter feeder so not to say that you must feed this sponge, but if you prefer to keep your tank rather "sterile" then you might want to give a daily or three times/weekly phytoplankton and/or zooplankton diet a try along with churning the substrate up weekly so the detritus can be carried by the current. Speaking of current, it should be directed towards the broad side of the plane/paddle. Some folks even use silica additions since this is an important part of sponge intake, which can pose a problem with heavy ro
users. This is a nonphotosynthetic sponge, but usually heralds from deeper water if I am not mistaken so I would lower it a bit? Hmmm, don't let algae encroach either, which usually provides a quick death. The white areas are probably signs of impending death due to nutrient loss, but these necrotic areas can also be cut; This is not a particularly hardy species of sponge (Stylissa?).