Hi,
Well, as in so many cases there is often some truth wrapped in some degree of hyperbole. In fact any nutritious substrate will do the job. There are many tanks out there that use other products and do just as well or better. While many people rave they often compare their current success using AS with previous attempts using some other substrate. What many fail to realize is that their
skill at plant growing prior to using AS may not have been as advanced as it is now, so they have excellent plant growth now and attribute all their success to the AS. Very few have actually done side by side testing, using their current skills and knowledge, to determine just how much difference AS makes.
Having said all that though AS is a better product than the rest in large part to the fact that it is a clay product which has been soaked in nutrients and organic matter (like peat perhaps) and then kiln baked. The clay holds a large amount of nutrients for a longer time than most other materials. Clay is also a particularly good material for plant roots because of it's electrochemical properties which facilitates transfer of metals and nutrient compounds to the root hairs. This property is called Cation Exchange Capacity (CEC). In addition to the nutrient store and material advantage, the grain size allows water to circulate between the granules.
So this is a good combination, but there are other high CEC and/or high nutrient products, but AS executes this combination better than most, is attractive, and is easy on the hands when planting. In a highly lit tank. It is not the be-all and end-all though, but merely part of a system. Look at this thread by JamesC using a modified inert substrate called Akadama while growing a difficult plants known as UG=>
viewtopic.php?f=3&t=749
Many people, including those using AS have been unable to grow this plant very well, yet James has been able to grow it using nothing more than a Bonsai substrate. Clearly therefore, there are a variety of factors involved in growing plants than just what substrate is used so it's best not to go over the top. AS is an excellent product with clear advantages and so is the substrate of choice, but if you uses something else that won't be the end of the world either.
Here is another example: The tank shown below is a large (6 ft), very highly lit EI tank (about 1/2 kilowatt T5 with reflectors.) To obtain the standard depth would have taken nearly 20 9L bags of AS which I felt was an abomination pricewise but I do like the look of AS. To create the proper illusion I filled the front 5 inches with AS and the aft 14 inches with inert gravel mixed with a bit of Ecocomplete (the tank is 19 inches front to back). This meant I only had to buy a half dozen bags of AS, and that only carpet plants would be mounted on it. In this photo you can see that there is good growth of all the non-carpeting plants. This amount of growth took less than 5 months. The distance from top to bottom in this shot is about 24 inches.
Now let's see an example of what AS is
not capable of doing in this tank: I left town for about 5 days forgetting to a) dose extra and b) reduce the lighting. Normally PO4 is the first to bottom out in this tank so when I returned from my trip the tank was covered with GSA. Look at this plant that is rooted in 100% AS and see if you can tell from the leaves at what point the water column was returned to regular dosing.
So this demonstrates that
no substrate is capable of preventing nutrient deficiency when the tank is under duress from extreme lighting. The environmental pressures and nutrient uptake demand are simply too high. It required about 5 weeks of normal water column dosing to get the tank back into reasonable shape. Therefore if you have access to AS then get it because it is as good or better than you will find but if you choose something else then that's not a big problem either. It's more important to understand the science of what is going on in the substrate and the rest of the tank in order to make the proper adjustments.
Hope this helps. 8)
Cheers,