Help/advice needed

[ReEf BoSs]

When i reused sand, i put it in a 5 gallon pale and rinsed in the bath tube turning it over until it stopped looking like dirty water. It worked okay. If there is currently no life in the tank you cant go wrong by trying if you need to . New water and time and it will all work. Id just clean everything as much as possible firs that way you’re not fighting high nutrients forever

[hillegom]

Good advice with the sand. Thats what I would do. Cheapest. There will be some nutrients left, but you could deal with that when you cycle for 30 days.
As well, I would clean the rocks. either pressure wash or soak in acid. I can't remember what kind, but someone will chime in here. The dried algae will put a lot of unwanted nutrients into the water column.
You could cycle the rock in a couple of 5 gal buckets and a power head.
Good luck with it and glad to see you are coming back into reefing