Hello; It also appears that the floor may have carpet. My experience with carpet and aquariums was not good. So bad that I will never again consider having tanks on a carpeted floor. I understand that many still do so, but it seems to lead to problems. Small spills will happen all along and the carpet will stay damp. A big spill or leak can and has damaged both floors and carpet. Either way there will likely be mold/mildew in the damp carpet.
The carpet will also stay wet from spills for a long time and may weaken the structure of the stand especially if the stand is a pressboard (glued wood chips) of some sort.
On the sand being cloudy. I started sifting sand while dry thru colanders or homemade screen boxes. This way the very find dust can largely be discarded and some desired size of sand grains can be had, depending on the screen size. After dry sifting a good rinsing of the sand with a hose and a few spare buckets will get rid of more fine stuff. As hte tank sits the fine stuff will be an issue for some time to come. The fine stuff will be stirred up pretty much all the time for a considerable time. It has also damaged the internal parts of filters over time as the stuff is abrasive. As the consensus appears to be that the stand is in question and perhaps should be replaced, that would be a good time to give the sand a good rinsing when the tank is redone.
Good luck
anyone got any idea how long it will take? 
