I feel ya on the yellow water. My biocube that has been running for about 20 years has the same issue. No matter how much water I change, it is almost immediately yellow again. I chalk it up to the rock just being completely loaded with organics after years of neglect. One of the main reasons nothing but the fish will be transfered to the 60 gal cube when it is finished.Seems the abundant dieoff has kicked off a bacterial bloom and mini cycle, which explains the still-cloudy water and unhappy corals. I will say that in spite of all the troubles, it’s been quite a while since the water actually smelled like a proper reef tank and doesn’t appear with a yellow tint.
PS I love the smell you are talking about! Although I can't really smell it much anymore due to my bout with covid about two years ago. My sense of smell never has fully recovered. My wife would look at me funny when I used to stand over my tank and take a big whiff! Lol