My quindecim] once did this after I put in too much beech leaves.
According to Anton Lamboj (an ichtyologist) paros do not possess a labyrinth organ, in contrast to all other Macropodusinae. He dissected quite some of them but did not find any labyrinth organ. He said it was severely reduced also in Malpulutta, and to a lesser extent in Trichopsis, while Pseudosphromenus and Macropodus had an okay one, and Betta a good organ.
I only use a filter when I have really big amounts of leaves, to prevent oxygen deprivation. Otherwise a tank without too much fish really doesn’t need a filter. Out of my nine tanks only two have a filter running at the moment.
I would suggest you to take out most of the leaves, but don’t boil the rest. You’ll destroy the cell structure, making decomposition a lot easier. Leave in a part of the leaves and add an air pump. Wait for a week or so and put in more leaves. Repeat until all leaves are added, and then remove the air pump.