Hi all,
I use akadama in some tanks, and sand in others. (I'm cheap!)
Same here, if you want a low nutrient, low TDS system, or to exclusively use frequent water column fertilization (EI with dry powders etc) silica sand is a good substrate, it is inert and is purely a physical medium to anchor the plants in. If you want a media which will act as a "nutrient reservoir", you can use an inert medium (like sand, Akadama or Tesco's light-weight cat litter) and add slow release nutrients or you can use a nutrient rich media, either one which is a complex mixture of components (like garden soil) or an inert medium with fertilisers added (sand and Osmocote for example) or a designer mixture by ADA etc.
How "good" that medium will be depends upon a number of factors, but probably the most relevant are the CEC and AEC (Cation Exchange Capacity & Anion Exchange Capacity), this is the ability of that substrate to hold and exchange ions (nutrients Mg++, NO3-) from solution (the tank water). Clays and humus for example have large CEC values and silica sand or perlite have no CEC. Clays retain some CEC when they are heated, this makes them physically more stable (think of brick or porcelain). As a general rule clays calcined at high temperatures are very physically stable, but with much reduced CEC, those calcined at lower temperatures retain more CEC, but are less stable.
My personal opinion is that your plants and shrimps can't read, and have no interest in aquascaping or human aesthetics, therefore the choice in these areas is entirely yours. Purely in terms of plant growth I'd use the cheapest substrate that fulfils your requirements. For me that is either an inert medium (sand) or a medium with some CEC, (Sand + clay + humus) or a calcined clay based media that is physically reasonably stable, but retains some CEC, like Akadama, lightweight cat litter etc.
cheers Darrel
