The photo would show how the substrate looks from the front of the tank. Wouldn't matter how murky the water is. You can load your photos in Photobucket.com or flickr or another photo hosting site. Then just copy the link and paste it in your post here.
5-1/2 inches does seem pretty deep. Is that just the sand? If it's too deep, you can take some out using a cheap turkey baster. Just squeeze the air out of the bulb and suck up the sand, then either take it out of the tank or move it elsewhere.
Assassins will burrow in just sand. And they don't eat more than one or two pond or ramshorn snails per week each. Just don't overfeed your fish and you should be fine.