Well, there may be issues with individual batches, and I recall you have had some difficulty in one or more of your tanks, which you attributed to Amazonia, but I don't think think it can be said that unilaterally, Amazonia is problematic. There are just too many successful tanks out there using Amazonia to bash it without further evidence. I've never had a problem with Amazonia. George Farmer, Dan Crawford, Viktorlantos, just to name a few, consistently turn out brilliant aquascapes using Amazonia and it's my favorite substrate, except for the price!
I also don't think that it can be demonstrated that Amazonia has any effect on CO2 dissolution. There are thousands of tanks which suffer poor CO2. In fact, poor CO2 is the single biggest cause of the demise of most unsuccessful tanks, regardless of substrate choice. It would be difficult to imagine, by what mechanism this substrate could reduce the CO2 concentration level of the water column. The CO2 concentration level can only be a function of pressure, temperature and NaCl concentration. Clearly, pressure and temperature are not affected by Amazonia, so if it can be shown that the NaCl level of the water is significantly affected by Amazonia, then it would be believable, however, the level of NaCl sufficient to affect CO2 dissolution would negatively affect the health of freshwater fish, and this would be consistently observable.
As you've mentioned:
Which is a valid statement. However, it should be noted that organic substrates such as soil and leaf litter, do generate CO2 because of the bacterial metabolism facilitated by the high levels of carbohydrates found in soil. Amazonia attempts to replicate this phenomenon by infusing peat or similar carbohydrates sources on the baked surface of the pellets. Plants that are capable of CO2 uptake from their roots can take advantage of this mechanism. So actually, there is some relevance in of CO2 in the sediment, but it depends on the sediment type, the preparation of the sediment, and on the type of plant.
I think Andy D's point was that when plants are grown in a terrestrial format, such as in the nursery, the substrate used, such as stone wool, has less relevance because the leaves have access to atmospheric CO2 and that nutrition can be applied either via foliar spray or by application of the nutrient to the wool.
It is reported that TMC Nutrisoil is a similar in construction and formula to Amazonia, but no details have been made available.
I agree that the high ammonia content of enriched substrates such as Amazonia is problematic, but this can easily be averted by simply letting the sediment sit moistened for a month in a bucket, or by baking it in a over for a few hours at over 200 deg.C. This will mineralized the ammonia into NO3.
Cheers
