Help me reset this tank

[MrChris]

Hi everyone. I am new to saltwater and need a little guidance.
I picked up a fowlr tank from a guy on craigslist a few weeks ago and have been working vigorously to whip it back into shape parameters wise.
I have suceeded in that aspect, and I am ready to start adding some corals once my lights come in.
Problem is, the live rock in the system is hideous. 3 different kinds of rock, some white, some really dark, and just not pleasing to the eye.
The bed is also ugly in my eyes, and definitely not adding anything biologically speaking. It is a crushed coral of some sort I believe.
So how do tear this tank down, remove the bed and replace with new sand, as well as adding new rock to the mix, all while keeping my livestock alive and well.
Will I need another aquarium, or will rubbermaid tubs suffice? Will I need filtration in these "holdover tanks" or will water changes suffice?
Should I not worry about the color of the rock itself? Will it get completely hidden over time anyway?
Will I be be starting a whole new cycle? How long will I need to hold my fish over until I can put them back in the display tank?
Like I said, I am new so sorry if these are stupid questions to you, but thanks yo anyone who takes the time to add some input.
The system is a 75 gal with a 20 long sump / fuge.
I will add some photos to help explain how it is set up.
Thanks!!!

 

[Crabs McJones]

First of all, Welcome to R2R!!

#WelcometoR2R

If you're changing out all the rock and the sand with new stuff, you're tank is going to need to cycle again. All the beneficial bacteria is located in the sand and rock and not so much in the water. You can transfer your fish and everything over to tubs with the old rock, and as long as you have a heater and some sort of water movement (powerhead or wavemaker) they can remain in there for an extended period. But don't transfer over or reuse any of the old sand or crushed coral substrate. Others will chime in with more information for you. But again welcome, and take lots of pictures, we go crazy for pictures

 

[PatW]

You could use a several of approaches.

One, you could get a food safe container like a Brute trash can, which is handy to have. Put some of your old rock in it with the fish, a powerhead, small light if you wish and a heater if needed. Then pitch the old rock and substrate, add the new, and cycle.

Get your new stuff with the powerhead, Brute trashcan, etc and cycle it all in the Brute trashcan. When it is cycled, remove the old stuff from your aquarium and add the new. You might not even need to cycle the substrate just add it after repeated rinses.

Or you could just add the new dry rock a piece at a time over a period of time. It will cycle in an established aquarium.