While it is often recommended to add salt to the aquarium for mollies, it is not necessary as long as the pH is kept between 7.8 to 8.3 with a alkalinity between 90 (5 dKH) and 160 ppm (9 dKH) and a hardness at a minimum of 300 ppm (17 dGH), but closer to 600 ppm (34 dGH) would be better. If you are keeping live plants with mollies, choose plants that like hard alkaline water.
All these livebearers can benefit from aragonite, dolomite, calcite, limestone, coral rubble, and snail shells being placed somewhere in the aquarium ecosystem. Calcium based material can alternatively be placed in a filtration system away from the main display. These materials will slowly break down in freshwater, adding to alkalinity and hardness.
Labyrinth fishes from Asia are colorful and behaviorally fascinating fish to keep in the aquarium. Most prefer a low flow system, with a calm surface for building a bubble nest for spawning. Many of these fish will show their best color in a planted aquarium. There are many man developed color strains of the many different species of gouramis and bettas.
Floating plants like water sprite (Ceratopteris pteridoides), Riccia fluitans, and duckweed (Lemna minor) are often the choice for gouramis and bettas, as they will use the plants for anchoring their bubble nest. Depending on the size for the fish, these bubble nest can range in size from 2 to 6 inches (5 to 15 cm) or more. Floating plants will need to tinned out on a regular basis, as they can multiply quickly and prevent the light from reaching the bottom. Duckweed can become a pest plant in the aquarium, because it reproduces quickly, and sometimes is difficult to eliminate.
Bettas and dwarf gouramis can be kept and bred in 10 gallon aquarium. Aquariums should be heavily planted to allow fish to hide in case of aggression. Larger gouramis may require a 50 gallon or larger aquarium.
For most of these fish a pH between 6.5 and 7.5 is adequate, with soft to moderately hard water is acceptable.
Most Central American cichlids we see in the hobby come from rivers with moderately hard water. Calcium carbonate rock is common in the area where many of these cichlids are found. The majority either spawn on rocks or in caves. Aquatic vegetation is often very limited in their natural habitat.