Is My Tank Overstocked

[Rayq]

The 50% a week water changes are only for when the filter is cycled. Until then you need to do big daily water changes. You must stop both ammonia and nitrite from ever getting as high as 0.25. Once the filter is cycled, the bacteria will do it for you. Until they have grown, you need to keep them low by doing water changes. That could mean every day for up to 2 months.
Just to check - you do have a filter?

We also need to know exactly how big your tank is to advise on stocking. The dimensions you gave in an earlier post don't sound like 3 gallons. To give you an idea, a tank 12 x 8 x 8 inches is 3 gallons. You only gave 2 measurements; we need the third to calculate the volume. We need side to side, and front to back, and top to bottom - with top to bottom, that's the water surface to the bottom of the water.
If your tank really is only 3 gallons, the fish you say you have in there would be jammed in with no room for them to move properly.

I do have a filter. Yea I thick I calculate wrongly. It's shows 3.33 US Gallon. 2.78 UK Gallon. I wanted to get one bigger tank but I just can't find one. I'm in Malaysia and every tank i found was more than RM50 for about 3-5 gallon. ( 15 dollar , at your place I guess) and I heard that you could buy one 10 gallon with that. I found many 10 gallon ones but thier more than a hinder ringgit. So I didn't bought one. Now I'm saving money for that.

 

[Essjay]

If your tank really is only 3.3 US gallons, you need to rehome all the fish you have as they are not suitable for a tank that small. The only fish you could possibly get away with is a siamese fighting fish. You could use it as a shrimp tank instead, their are quite a few colourful shrimps.
Unless you can get a bigger tank - and with the fish you have you need more than 10 gallons - I would either take the fish back to the shop or give them to someone who has a bigger tank, then cycle your small tank and get a siamese fighting fish. If you can't get a bottle of ammonia for a fishless cycle in Malaya, it is possible to use fish food or a dead shrimp (the kind you eat). Both decompose to make ammonia.