How long has the tank been running with fish in it ? what water conditioner are you using?
If this is an (uncycled) new tank of less than three weeks, You will need to perform near daily water changes of two to three gallons replacing that which you take out, with clean water that has been treated with dechlorinator such as PRIME or AMQUEL+ those are full function water conditioners that will detoxify ammonia from fish poop and urine which if left in the tank, will kill your fish within days if not hours. I too would remove all but the three tiger barbs to help keep waste levels low until the tank matures or (cycles) I would feed the fish once every other day and only a pinch of food. This will not hurt the fish but it WILL help keep toxins such as ammonia and nitrites from killing the fish. I would also purchase a test kit such as the API freshwater master kit So that you can test the water for ammonia and or nitrites and change the water when levels become dangerous. You can also have the fish store test your water ,,most will do it for free if you bring them a sample, but I would NOT take that sample to the fish store that suggested the shark and the clown loach. Clearly they are not to be trusted with respect to properly stocking a fish tank. Plenty of folks here to help you ,just ask. Not everyone should half to learn the hard way through sick and or dying fish ,,how to set up a trouble free tank with fish that will actually thrive as opposed to die.
In order of impotance,, I would purchase one of the two water conditioners mentioned,, And I would purchase the test kit. The one mentioned is used by many but even the strip style tests which aren't all that accurate, will give you a ball park figure and help prevent lost fish. You will also need small handheld gravel vaccum to use for removing the water and sucking up any uneaten food or fish waste (poop). The shark and clown loach absolutely won't work in a ten gal tank. Both are shoaling species that need to be kept in groups and need plenty of swimming room. While they may do ok in something like a 55 gal when young,, they will need larger tank on the order of 75 to 125 gal with larger being better when they reach five inches long. But don't take my word for it, google information on the species of fish before you go shopping for fish and in this way,, you will have some knowledge about the fish without relying on ignorant fish store employees .