You have a 13 hour photoperiod, which is very good. So it's not that.
Since you lost your floating plants, that suggests an iron deficiency in the water.
Did you use compost? Real mineral soil contains plentiful iron, but pure organic material like peat does not. If so, it could be your tank is deficient in iron.
I would add a micronutrient fertilizer and/or chelated iron. Try again with floating plants. Your goal should be to have enough nutrients in the water to grow floating plants.
Your rooted plants may be getting just enough iron from the substrate mulm to keep going, but not enough to thrive.
Manganese is another micronutrient that oxidizes in the water, so if your substrate is gravel/compost, start out first with a micronutrient fertilizer. Then, you could go to a chelated iron powder, which is cheaper.
I think Ember tetras would be fine with a Betta.