Wiggles good job - I trained you well padiwan.
Willz - sounds like you are off to a great start to the saltwater side of the hobby. Love to see you putting in effort to go about this the "right" way.
Its fine with the water in there now.
I would wash your sand very throughally (with freshwater will be fine) and add it to the tank in small portions.
Most of your bacteria is on your rock anyways - and this gets rid of any detritus that your sand is holding that will effect h2o quality in your new setup. In addition it means that you can get sand into your tank without making too much of a mess in the way of cloudyness. This is how I filled my 125g mixed reef - I had just torn it down literaly hours before and it was a old DSB tank. So if anything was going to make a mess - it woulda been this tank. I just washed very small portions in an ice cream pail and added them slowly.
Willz - sounds like you are off to a great start to the saltwater side of the hobby. Love to see you putting in effort to go about this the "right" way.
Its fine with the water in there now.
I would wash your sand very throughally (with freshwater will be fine) and add it to the tank in small portions.
Most of your bacteria is on your rock anyways - and this gets rid of any detritus that your sand is holding that will effect h2o quality in your new setup. In addition it means that you can get sand into your tank without making too much of a mess in the way of cloudyness. This is how I filled my 125g mixed reef - I had just torn it down literaly hours before and it was a old DSB tank. So if anything was going to make a mess - it woulda been this tank. I just washed very small portions in an ice cream pail and added them slowly.
No matter how I tried it, it wasn't going to fit without cutting out a center brace, and I wasn't about to do that. GF gets back with the trash can. Discuss sump situation with GF. Decide to put sump behind tank, which means moving tank out 18" from spare bedroom wall. Start a siphon to get the new water out of my tank so I could add the sand and move the tank. Ran to Lowes to get some tubing (his was kind of shot) for the return pump. Got home to find the trashcan WAY bowed with 40G of water in it. Got panicked quickly moved the tank out from the wall and added his sand. Put the card board over the sand and started pumping. Huge mess. I really don't think this guy cleaned his aquarium in like 5 years. Once I had the trashcan empty I started "stacking" the LR in there. By stacking I mean blindly putting the chunks of rock into the tank as it was Burning Man sandstorm visibility in the tank at this point. Had a ton of LR that I put into the refugium since my tank is a 75 and his was a 90, I just didn't need all of the LR in the display. Got the sump running. Couldn't figure out the skimmer 3 beers into the night, so I cleaned an AC110 and added the carbon insert to try and get some mechanical and chemical filtration going. The sump only had a filter sock and LR which seemed lacking in the way of mechanical/chemical. About midnight I check on the fish bucket and weigh the pros and cons of leaving them in the bucket, which was looking and smelling nasty, or adding them to the tank, which was still super cloudy (cloudy doesn't even begin). Since the temps were balanced I checked his water's salinity and was surprised to see it was at 1.019, the stuff I had mixed up was at 1.023. Decided to do a drip into the bucket from my tank to hopefully acclimate them to the water. By 2am I added the fish and called it a night. 
