Marineland and Seachem make some very good carbon type ammonia removers. If you can run these in your filtration, do so. This ONLY addresses the symptoms, water changes will address the cause.
Water change , water change, water change, test, test, test!
That Dogface puffer really needs a tank of 90+ gallons for the long term. They excrete A LOT of waste, which might be the reason your parameters are off. Consider beefing up the biological filter with more live rock, better filteration and vacuuming the portion of substrate you can get to.
Most inportantly, address the cause for the long term, address the symptoms in the short term.