Well I do have some good news. Last night I did a small water change with one 5 gallon water jug I had lying around. I have to do more I know but the ammonia has dropped a small amount. Its about 0.40, but I see some change in the neon tetras. They seem to be swimming all around the tank, compared to yesterday when they just sat in a corner. Last night I did take out the sarpae tetras because they were nipping a lot. I also took out a black molly because he seemed weak, and 1 neon that most of his tail was gone. I think I might see some new skin on the tails of the neons. I did add about a tablespoon of salt also. Hopefully If I get the new filter and do a few more water changes, the fish will be healthy and happy.I think upgrading the filter if you have a possibility is a good idea for the size of the tank. 125G/h is about 475 litres an hour and personally I think this is quite low for a 29 gallon tank, especially considering it is not even working properly.
Keep us posted how the fish are doing