You added Otos a short time ago, right? Any oto that dies within the month of purchase is usually due to the whole catching-selling-traveling thing. They come into stores absolutely wrecked.
Other than that, the tank looks great. With any walstad, in my limited experience, less is usually more. When it comes to plants, avoid at all costs cutting or trimming large amounts at a time. It's the equivalent to squeezing a filter sponge too much, they keep the thing healthy. Your fish are breeding, si it's a healthy environment for sure!