Dark blue with yellow tail, sounds like a blue tang to me.
Honestly, what you're looking to do will take a few weeks to do properly. Before doing anything, take those fish/animals to the LFS
and sell them for a credit, OR ask them if they can hold them for you for a few weeks.
Ask your LFS
for some large styrofoam containers with lids, most seem to have these sitting in the back room. Use this to move the live rock, with the lid on they will maintani their moisture for a few days even.
Buy a good RO
system and start making fresh water for the aquarium. You'll need some large containers (I use garbage bins) to hold the water while it's being made.
Dump all that water out of the aquarium, don't bother bringing it home with you. Empty everything frm the aquarium, as a 210g even empty, is heavy. (rocks, sand, ornaments, water) Don't worry about cleaning anything until you get home.
Use a gravel vaccuum to clean the cyano
off the sand before removing it. Other than the cyano
on top, the sand seems to be in good shape to be used after a few rinses.
Once you got everything home, you can use an algae scrubber and some fresh water to clean the glass, it's better to rub lightly 5 times then hard once and risk scratching the glass. I find it easiest to do this cleaning with the aqurium sitting on the floor, so you can walk all around it and clean it properly.
Next, start scrubbing some of the nuisance algae from those live rocks in those styrofoam containers.
You can clean/rinse the live sand in some freshly made SW
. You'll never get the water crystal clear, you just want to remove the large waste particles and algae from the sand.
Then you can begin cleaning that sump and skimmer out. Bioballs work great as long as they're NEVER moved. Move them and you'll have problems. Either rinse them out and start fresh with them (don't remove ALL the stuff from them, there is tonnes of beneficial bacteria on them), or get rid of them and buy some Live Rubble to use in there instead. (or a 50/50 mix, and down the road you can start removing the bios for rocks.)
Clean out that skimmer really well too.
Next you can hook everything back up. Then, head to your local hardware store, or LFS
store... because there will be lots of parts you'll want to replace or upgrade at this time. (plumbing, lighting, filteration, etc.)
Put in your live sand, live rock, and water. You can mix the salt in the water at this time.
You'll need to wait a while for your tank your cycle, it shouldn't take too long though. My tank had a lot of stuff from a preexisting aquarium as well.. (rock, sands, etc.)... it didn't even take a full week to cycle, and during that time my LR
came with a blenny, some starfish, hermits, and snails, and I have't had any fatalities either. So it shouldnt' be too bad.
Next, you can start introducing your fish back to the aquarium.
And last, you can enjoy your new free aquarium.