To avoid misunderstandings, there are 3 kinds of soda :
All three are "pH buffers" to some degree.
1. Baking soda or NaHCO3
= Natrium bicarbonate (EU) or Sodium bicarbonate (USA)
pH = 8.4
I use it for my koi-pond to buffer the pH at 8.4 to prevent pH-crash.
Coincidentally, the water purifying bacteria in the biofilter have the best performance at that specific pH.
http://home.casema.nl/galaxy/nitr_ph.gif
I dump a couple of pounds in the pond monthly.
When people are worried about the health effects on my fish, i dip a wet finger in the stuff, and bring it to my mouth.
If it doesn't harm me, then it shouldn't harm my koi.
If i have problems with stomic acid, then i eat a teaspoon.
2. Soda, or natrium carbonate or sodium carbonate or Na2CO3
pH = 12 Do not eat !
Used for household & cleaning purposes.