To add to shaun's exellent comments, i'd also stress the following.
Decide what you want your sand bed to do...do you want it to be a nitrate reducing area or not.
If you do, then idealy you need to remove any agressive sand movers and switch to more passive sand sifters such as cucumbers that will 'gently' work the upper sand layer, without impacting on the fauna thats needed to make the bed function effectively lower down.
Agressive diggers etc constantly disturb the o2 depletion ratios and dont let the bed settle into a consistant rate of diffusion. They also impact on the diversity of the bed, lowering the amount of burrowing action required to free up the sand structure and draw water and nutrients into the bed effectively so they can be broken down to harmless nitrogen.
another words, too much action can be just as bad as too little as far as substrates go 'if' you want them to settle and become effective nutrient converters beyond Amm-N02-No3.
the key, is diversity, stability, and 'gentle' movement to free up the grain structure and prevent it binding which is where your critters and the cucumbers come in.
Regards