I just saw Kent Marine homepage and they state that their liquid calcium formulation will not affect pH or buffering capacity (KH,
GH in freshwater).
You already have a pH of 8. I guess it is safe to use but I don't see the need for it. You have plants that come from natually hard-water environments, as well as some of your fish, except for the Gouramis.
Most likely, if you used baking soda, the most your pH will rise is likely to 8.4 or 8.6 (I don't recall exactly).
Calcium is usually available as needed in
FW tanks. Unless you use mostly water collected from rain, use R/O processed,or otherwise demineralized water.
Peter Hiscock, in his book Encyclopedia of Aquarium Plants (2003), page 72, notes that Calcium is a macro nutrient for plants (they need it in relatively big quantities, not as trace elements). he refers that calcium is most likely present in sufficient quantities in most water supplies. He warns to be careful when adding Calcium since an excess will limit the availability of other nutrients (for plants at least) and raise, as SWilkins said, the hardness of water.
That said, some claim (like Carl Strohmeyer, for Americana Aquarium Products, if I recall accurately) that not all calcium measured (as in calcium carbonate tests: CaCO3) is actually bioavailable and therefore a slow release of calcium in ionized form (Ca++) is a good idea (then again, he sells "Wonder Shells", a product that does precisely that but I trust him).
I keep invertebrates (various types of snails, FW clams, Yellow Nose Shrimps, FW craigfish) in diverse tank settings, from soft to mid to hard to low-end brackish.
My Apple Snails growth rate is indeed slowed down by lack of calcium (from the same hatch those in soft/acidic water ended up noticeable smaller than those in other tanks).
Pepe
Santo Domingo