Help with white growth

[Clowning_Around]

I've had my tank up for about 8-9months now 2 of which have had livestock. I just recently had the new tank syndrome with brown algae diatoms everywhere. Theyve just recently started dieing off rapidly and all livestock still looks good. I do have a little areas of detritus scaterred in pockets across the sand bed that i had intended on vacuuming this weekend but tonight i noticed they are all covered in this white growth (see pic) it looks fungus like but i have no clue what it is or if it is a bad thing. Would someone please enlighten and advise me.

Thanks.

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[Clowning_Around]

Have been told this is just sponge

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