Hi Andrew, welcome to the forum!
I think your tank is really too small for danios.
Most of the commonly traded varieties of danio such as leopard and zebra, are extremely active swimmers and while they are not large fish, a tank of around 2-3ft is recommended by most of the better reference sites.
It sounds like your plants are terrestrial plants that were sold as aquatic, if you were told they would only last 2-3 months. If they are, I would remove them now as they will eventually die off if kept fully submerged, and this can cause issues with water quality. You are better going for plants such as lace fern, java fern, anubias etc. as these are hardy and will survive long-term under water. Terrestrial plants are just a way for stores to make more money off you as you then have to keep going in time and time again to buy new plants.
From your post I assume your tank wasn't properly cycled in advance? Do you have test kits for ammonia/nitrite? I prefer liquid test kits as strips can be pretty useless and give you inaccurate results.
Poor water quality is probably the biggest killer of fish in this hobby - particularly with new set-ups. Without test kits, you are basically going in blind as you have no idea of the quality of your water and whether you should be doing more or less water changes. Crystal clear water can be fatal to fish because you can't see the ammonia and nitrite building up, and you only need very low amounts to cause serious harm or even death to your fish.
Your danio's behaviour definitely sounds abnormal. My first port of call when something is wrong with my fish is to test the parameters and do a water change. If there are no issues there, I start to consider other possibilities such as disease, external/internal parasites or possibly that the fish may have issues relating to its time at the store prior to purchase.
I wasn't sure how new you are to this hobby, so apologies if some of this stuff you already know.