I guess I’m relatively new to the hobby and looking for answers. Part of that is understanding what my expectations should be when I make a change such as dosing nitrates. I’ve read through countless threads on these forums about low nutrients and they’re all the same. None of them document what the OP did to fix their problem, how long it took and what if any hurdles they had to overcome to get there. So when I see acros start to turn brown and rtn as a result of me dosing nitrates, naturally I’m concerned and looking for answers. I apologize if this is all so simple to you seasoned pros.
Your acros are not turning brown and RTN because you dosed nitrates. They are doing this because they have been starving since you introduced them into the tank. What you did yesterday doesnt cause this. Its what you havent been doing for the weeks/months before thats causing this.
Your corals are starving. Your dose of 0.5 ppm is a drop in an ocean.
You need to get to a point you can actually register the nitrates and quickly.
Newer tanks are not the same as older mature tanks. Older tanks can run with really low nutrients because there is usually a ton of flora/fauna, coral, bacteria etc etc consuming and creating nutrients. The import is very high and consistent, well the export is enough to keep the detectable levels low.
Newer tanks do not have this balance. You need to have those nutrients present cause there is very little available and the little that is available will be taken up by bacterias and algaes much better and faster then any coral will get it.
Dose you tank with enough nitrate to hit 3-5ppm nitrate and 0.03-0.05 phos daily and test regularly to see where you are at. I would try to get to the point where you are in the 10ppm nitrate and 0.10 phos range. If you still arent registering anything you need to dose more. when you hit these numbers or exceed them adjust dosage accordingly to maintain it. I would also take the refuguim offline entirely. Its only working against you right now.
There is more nuance to this then can be said in a simple forum post but hopefully this can help you.
The suggestions for more fish is also very valid.
Ill finish this with the statement, this is my opinion alone, and is exactly what I would be doing if I were in your situation. YMMV