My Christmas moss and weeping moss did brown out for a while then became stable.
Mid they AR light demanding plants then they will also be co2 demanding. Whatbis your current co2 dosing? Also what ferts are you using and how much? I'm using the neutro+ range and it's showing good results so far. Although I feel the root demanding plants such as bulbs and swords need root tabs with them. Temperature is also key. Keep it cool is the best to stop excessive melting and optimal growth. I think between 20 - 26 is best although I'm at 28 as I intend to introduce discus eventually. (Might be a huge mistake 😉 at lower temperatures the water holds and exchanges gases with the atmosphere, much easier than at higher temperature so it's richer in co2 and O2. I'm thinking that the co2 needs to be at least 25ppm but for you 30ppm would be better as its starting out and already struggling. How do you inject co2?
Found your link above at the top to your tank...
Looks like great flow!
Now the melting has stopped maybe more nutrient is required. Just keep an eye on algae or good regular water changes. Would love to hear how this recovers.