Argos playsand is fine, but expect to be syphoning off the noticeable poop regularily as it really shows it up. Of course you can mix in some gravel, but I'm wondering why you would want to do this?
As for the depth, it depends on whether you are growing plants or not. I had 1 1/2 - 2 inches of playsand on top of some first layer laterite for the plants.
As previously said, stick some in a bucket and run water into the bucket until the cloudiness goes. Don't overfill the bucket though or it makes it tricky if you want to swirl the sand around a bit.
I have recently changed to Maidenhead Aquatics fine black gravel. A bit bigger than sand, but looks smart and is easier to keep.
Squid