Hey I see it's a fifty gallon system and this will be it's first deep clean. that's the max size we like to work with, but lucky you, rip cleaning a 50 gallon isn't all that bad.
here's what I recommend, pics inside the link show what you will get.
for your tank and it's details, you need to disassemble and rinse out the bed like we do, study how we rinse sandbeds it's not your usual method.
Any opinions on what type of algae this is growing on my rocks and sand bed?
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then you hold that sandbed in a bucket and go set it in the pantry or something open topped, you won't need it for a while.
You would then run the rock cleaning, as we detailed in the thread, your rocks are now algae free
you would then assemble your tank back, minus the sand, with the clean rocks fish and corals, and all new water matching the temp and salinity of the current.
you would expect about 3 months or so of light growback management of the rocks, in a bare-bottom tank because you can keep those cleaner than sandbedded tanks, to make up for letting them blanket over like that / they're seeded well now so you will be occasionally lifting out a rock, and scrape + treat the algae off that spot before it grows back. You'll learn manual controls prevent all algae takeovers in the no sand tank, be removing detritus as it collects on the bottom vs in the sand grains now for three mos
manage the tank by hand, make the rocks look right, do normal water changes.
then you put the rinsed sand back in three months, you just simply add it in/it won't cloud you rinsed it.