I'm not an expert in the SW aquaria world, but I can answer that question hutch. The nitrogen cycle has three major steps (well, four, or sometimes five, depending on who you ask, but that's neither here nor there). Raw organic waste (i.e. dead shrimp) decays and releases toxic ammonia into the water. The first step in the cycle is the growth of bacteria which break down this toxic ammonia into slightly less-toxic nitrite. When this happens, ammonia levels drop rapidly and nitrite levels rise rapidly. The next step to happen is the growth of bacteria which convert nitrite into even less toxic nitrate. When this happens, nitrite levels drop and nitrate levels increase. Your final step is the removal of the nitrates. There are various methods to do this, but the simplest and most effective is to perform a water change, and keep performing them on a regular basis (biweekly seems to be what people say).
I would remove the shrimp from your tank if you haven't already, as the ammonia-converting bacteria have already propogated. If your nitrites are still high, the tank hasn't fully cycled yet. When they reach zero, do a water change and you should be good to go. Make sure however that your tap water (if that is what you are using) does not have added nitrates (you can do this by testing the water, or by calling the treatment company). If it does, purchase RO/DI water (walmart, lfs, or buy an RO unit) for the water changes so you aren't adding nitrates with each change.
As far as carbon goes, various filter types come with carbon already in the media. If yours does not, or if the carbon isn't doing a great job (with yellow water, it probably isn't or isn't there), you can purchase activated carbon from a lfs and a bag to place it in (there may be cheaper methods for bagging the carbon, but that's not my area of expertise atm). Rinse the carbon to remove dust, fill the bag, seal it, and place it in your filter. It will need to be placed in different areas depending on your filter type. Make sure to place it where the flow out of the filter (before the water actually exits the filter though) passes through it. The carbon will remove various elements from the water, which should hopefully remove your yellow color, unless there is some other cause.
