Well, I just don't want to jump the gun and assume it's dirty water. Especially since I don't see any filth like I would in a dirty petstore cup. Everything in the tank seems fine too, so I'm assuming the water quality is okay.
Could be BWE. Could be that the sand made the water murky. Could be some other reason. We don't know since the OP hasn't actually told us, so I'm just going to wait on that before I complain about dirty tanks.
Not to mention OP is quite good at taking care of his/her fish so I highly doubt s/he'd leave a tank dirty, or even show it to us if it were.