[Ninong]

Originally Posted by bguile

I was at my LFS yesterday picking up substrate for my new tank and a few other items. I noticed on the Sugar sized Carib-Sea Aragonite bag it has the marking that says "Ideal for shallow beds and reef tank bottom cover". It looked like I had taken the last two bags so as I was looking around for more I found another bag of the slightly larger Aragamax Select that has a label that says "Ideal for deep sand beds....".

Carib-Sea gives you the average particle sizes for their various aragonite products here. Those are the dry products.

According to their chart, the average small grain size in their Aragamax Sugar sand is 0.1mm and the average large grain size is 1.0mm, compared to 0.5mm and 1.5mm for their Aragamax Select sand.

Carib-Sea is telling you that in their opinion the Aragamax Select is more suitable for deeper sand beds. Not everyone has the same opinion when it comes to what particle size mix is best for deep sand beds.

Before you decide which opinion is best for your situation, you need to understand why there are differing opinions. Let me try to make this as brief as possible by starting out with what many people would consider the ideal deep sand bed from a deep sand bed perspective without regard to other factors that might suggest a need for compromise.

An ideal deep sand bed would be at least 6" deep, preferably 8" deep. Right away you can see that this may not appeal to everybody for obvious reasons. The compromise position is that it should be at least 3.5"-4" deep. Already we're giving in to practical considerations and choosing a depth that is adequate but not ideal.

The ideal deep sand bed would be composed of a mixture of mostly very fine particle sands (preferably aragonite, IMO). Dr. Ron Shimek, and others, have written extensively on this subject. Here is an article from June 1999 in which Shimek explains his thinking on deep sand beds and suggests an ideal particle size distribution. Here is an article from June 2003 in which Shimek explains how sand beds really work. He has an expanded and updated version of this article in the October/November 2007 issue of Coral magazine -- the best hobbyist magazine in the world by far!

Dr. Rob Toonen has written extensively on deep sand beds here and here and more recently he has conducted experiments here and here, which resulted in conclusions that were surprising in some respects. A complete list of his publications can be found here.

Does it really make a difference as to which size to use to make the DSB more effective??

Yes.

I can understand that the slightly larger sand (NOT CC) would allow for less restrictive oxygen exchange at the bottom of the sandbed but is that necessarily what we want??

You don't want any oxygen at all at the bottom of a deep sand bed. You want a mixture of particle sizes that is conducive to supporting a wide array of sand bed infauna. In general, this would mean smaller sizes (sugar sized and smaller).

However, if you intend to run a system with extremely high water flow, you may need to take that into consideration in the design of your sand bed. A deep sand bed requires good water flow across all of its surface but it it may not be able to withstand extremely high water flow of the sort that some people are employing lately.

If you check around on the internet and in the popular literature, you will find hundreds of examples of very successful reef aquaria with a wide range of sand bed types. Even what can be called "deep sand beds" come in a range of types. I can point you to very successful reef tanks with 3" DSBs composed entirely of aragonite sand in the particle sizes described by Carib-Sea in their Aragamax Select product and I can point you to successful reef tanks with DSBs composed of sugar sized and smaller particle sizes in depths of 4", 5", 6", all the way up to 10".

I hesitate to suggest what is best for you. That's up to you to decide.