Your pH is too low
Your ammonia is too high probably due to your low pH
Your Nitrites are way too high, again, probably due to your low pH
No Nitrates, as a result of your bacteria not performing due to low pH

You need your bacteria to grow as quickly as possible, especially while cycling your system. They need a high pH, around 7.5, and lots of dissolved oxygen to multiply.

Your high nitrites may be what is killing your fish.

Oliver