I think your tank is going through its normal cycle if it's only 4 months old. The brown stuff might be diatoms and you usually get that with newly set up tanks. Do you have any snails or cleanup crew on the tank now?
You can also bring some of your tank water to Elos, Ocean Gallery or Pet Shanty so they can check if it's within normal range. They are all pretty close to your location.
You can also bring some of your tank water to Elos, Ocean Gallery or Pet Shanty so they can check if it's within normal range. They are all pretty close to your location.