OK, this is a marine tank right? If so, this post is in the wrong section, as this section is occupied by freshwater fishkeepers

Not to worry though, a mod will move it for you shortly if this is the case
First off,

to TFF.
Can you give us a run-down of water stats for ammonia, nitrite, nitrate, pH and phosphate please. Being a marine keeper, it is important, probibly more so than with freshwater tropicals, to have a good liquid regent based test kit at home. Marines don't tolerate any ammonia or nitrite in their water, but unlike freshwater fish, any detectable reading puts the fish in imediate danger

Any issues arrising, new fish or after maintanance you should idealy test the water to ensure no levels are up, so that you can correct them if they are before they stress or kill the fish, coral and clean-up crew
What water source are you using? (RO, salted tap or salted well water)
Is this tank bought new?
If so, it is probibly Diatom algea. Do you have any pictures? These will help greatly

If not, can you describe the yellow coating a bit more, i.e. hairly, slimy, dark or light yellow, where it is etc?
I'm not yet a marine keeper, but will be in the comming months, so am researching ATM. If this is a marine tank, click the "report" botton under your own post, and in the comment box, ask for the thread to be moved, stating that you accidentally put it in the wrong section. This will get you a better responce to the question more quickly as this will be moved into the other section
All the best
Rabbut