Issues with Nano

[Kabong]

Start of with a 25% water change.
Run some carbon if you arent already.
And you should really get some test kits asap

Depending on the size of your fish they are probably the cause of your problem. Ill presume there still young at this point, Since they havent killed each other yet. Just one of them at full grown is going to be pushing the max bioload on that size of a tank let alone 2 of them.

Are you running a skimmer of any type?