One point I wanted to pick up on was your mention of the pH and carbonate yields of a given sand. I thought the same thing for a long time, until I started chatting on reef boards and found out otherwise after reading some of the many articles by Dr. Randy Holmes-Farley (in the chem forum on this site). What I am meaning is, sand/aragonite from any source won't support pH or alkalinity in the sense we think of. The only way to support calcium, alkalinity and pH is to continually replenish supplies via any number of methods. The best ways for nanos seems to be any of the two part additives, small calcium reactors if you are really serious, or adding calcium/alk dosings from any of the major companies. Dripping in limewater is also handy.
Me personally, I use C-Balance from Two Little Fishies, Inc.
A quick reason why:
Your aragonite sand is the former skeletal structure of corals and other calcifying organisms. If it dissolved in water, so would our corals that lay stony skeletons behind as they grow.
The only way you can get chemical support from aragonite sand or rock is to have it dissolve to some extent in your salt water, but this is a problem because SW is already saturated with dissolved minerals and doesn't readily accept any more until you change a few factors---such as increase the solubility of water by dropping the pH (as in a reactor) or present your support in some other more soluble form other than aragonite. The calcium and alkalinity support we gain from additives is more soluble because its liquid and not housed in a crystalline structure such as aragonite. Somebody correct me if Im wrong here, trying to remember most of what Randy said...
For anyone who says they maintain pH and alk through their substrate alone, ask them if they have to replenish that substrate over time---they'll say no (pH of 8+ does not readily dissolve aragonite). Anyone who uses aragonite media in a reactor (pH around 6.5) will tell you they have to replenish it continually--because it dissolves in water. Most people who don't dose their systems and claim to use the sand as support have animals/corals that can tolerate the current measures of calcium and alkalinity components until the next water change--but they get no extra support from the sand.
So, Id say pick your sand based on the colors you prefer. There are some physical differences though, as finer sand will accumulate mulm faster on the surface but this is also easy to remove--and larger particles will allow mulm to seep into the depths of the sand making removal harder. Pros and cons exist for each, but in a nano it really doesnt matter all that much because we keep them so clean.
this is my two cents for today fellas.//./
I have no way of making short posts, its just not possible for me
brandon429