So, I came across this thread and it started to change my outlook on how sand beds work:

http://www.thereeftank.com/forums/f6...ed-160389.html

The gist of it is that everything, all the way down to the bacteria, poos and the best way to clean the poo is to siphon/clean the substrate. It goes on to explain that the side effect of poo left in the tank is phosphates.

Moving deeper, they make the argument that algae is not efficient at absorbing phosphates or other excess nutrients and reactors, that do not get fresh material regularly, add to the phosphate problem.

Since I have a small fishless tank that needs to be low nutrient, I've been following the advice presented and do not use anything but an ato. With weekly water changes and substrate siphoning, I have a healthy thriving sps reef. It's anecdotal for sure, but the above article quoted enough scientific articles for me to pause and really read what they were saying.