All good advice, especially the water changes, but the water needs to be good RO/DI water with the proper amount of salt in it. Ask the fish store you get your water from to show you their water filtration system and verify the TDS. I've seen several that only run RO, no DI, and that's probably not good enough. You also need to make sure the salinity is correct. I'd gladly send you a calibrated solution or you can make your own, just Google Randy Holmes-Farley calibration and you should find the formula.
What is "aquacultured" LR? That kinda scares me as it could be terrestrial rock that has been submerged in salt water for awhile. If so it could contain all types of crap you don't want. Unless you spent quite a bit of money on your Phosphate test kit it isn't likely to show anything unless your phosphate is unacceptably high. I don't think phosphate is your problem based on your description. The aquarium should have a slightly salty smell, not smell foul. Something is contaminating your aquarium is my guess and until you isolate it all the preventative measures you take are only going to help for a day or so. You might be better off removing everything into a "sterile" tank until you identify the problem. If you do and things improve, you've got your answer. If you don't you're likely to lose the corals so you have little to lose. There should be plenty of bacteria on the coral skeletons to keep things stable without LR unless you've got a ton of fish. IF you do set up a "quarantine" tank, just provide some water flow, a bit of RO/DI rinsed carbon from a reputable source, and something to keep the temperature stable. If your temperatures are like they are here and your AC is running, you may not even need a heater.
Good luck and hang in there. We've all done things in the past that resulted in losses but we learned a lot in making mistakes. You will too.
