What are the tank dimensions (length x width x height)?
Bala/ silver sharks can reach 10-12 inches long and need a tank that is at least 6 feet long. They also need to be kept in groups of at least 6 or more. I would probably return the silver sharks.
Rainbowfish need to be kept in groups of at least 6 (preferably 10) or more. Depending on the species of rainbowfish, they might eat the tetras, depending on the type of tetra.
Most rainbowfish do best in water with a pH above 7.0 and a GH around 200ppm.
Most tetras come from water with a pH below 7.0 and a GH below 150ppm.
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What is the GH (general hardness), KH (carbonate hardness) and pH of your water supply?
This information can usually be obtained from your water supply company's website or by telephoning them. If they can't help you, take a glass full of tap water to the local pet shop and get them to test it for you. Write the results down (in numbers) when they do the tests. And ask them what the results are in (eg: ppm, dGH, or something else).
Depending on what the GH of your water is, will determine what fish you should keep.
Angelfish, most tetras, barbs, Bettas, gouramis, rasbora, Corydoras and small species of suckermouth catfish all occur in soft water (GH below 150ppm) and a pH below 7.0.
Livebearers (guppies, platies, swordtails, mollies), rainbowfish and goldfish occur in medium hard water with a GH around 200-250ppm and a pH above 7.0.
If you have very hard water (GH above 300ppm) then look at African Rift Lake cichlids, or use distilled or reverse osmosis water to reduce the GH and keep fishes from softer water.
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