my black tetra started spinning about 2 days ago?

So manythings can go wrong with any animal, especially ones that don't see a vet. you can try to feed him the insides of shelled peas, if the problem is swim bladder that will help, if it is not swimm bladdere it wont hurt anything.

you need to get the results of tests for ammonia, nitrie and nitrate.

a cycled filtered tank is necessary for all fish, and tetras are especially sensitive. If your tank is not fully cycled it is not likely that any of the tetras will make it. a petshop will test the water for you for free, but you should get the liquid test tube kits so you can do it yourself. Since many petstore use cheap paper testers that can give false readings. And it is important to know what the tank parameters are for ammonia, nitrite, and nitrate. Ph is important to know too, but it doesn't change much unless you change the water source, so you don't need to test it as often.

you should have zero ammonia, zero nitrite, but not zero nitrate. Nitrate should be kept around 20 or less via partial water changes. , not over stocking the tank, not overfeeding...

Hi Teena

I feel sorry for your fish. It is hard to tell diseases in fish and treating them. One tip that might come handy is

try feeding him some peas. warm the pea and break it into small pieces or smash it and leave it near to the fish. It might eat some of it. Try this for a few days. If the fish is suffering from any indigestion the pea will act like a laxative and free its intestines.