Sorry you are having troubles.
You need a source of ammonia to cycle a tank. Some folks use fish. I prefer and recommend fishless methods as it is kinder than subjecting the fish to ammonia toxicity. Ususally if these fish survive the cycling process they are returned to the LFS only to be again purchased for cycling….. on and on until they finally most likely die in someones tank. A piece od shrimp or actually bottled ammonia can be used to cycle a tank.
It sounds like your tank did not cycle, unless you had some fully cured live rock in there. I have set up tanks in the past with live sand and fully cured live rock that never went through any sort of cycle.
If this were my tank I would stop feeding dead food. It is only adding to your problem. Feeding live red feeder shrimp from OR would help. They can live in the tank until eaten thus not contributing to the ammonia problem like dead food would by decaying in the tank if you can not remve it.
I am not a fan of adding chemicals to decrese ammonia. All these products do is bind the ammonia and I find cause other problems later. The only way to remove the amonia is to do water changes or add additional biofilter that will actually convert it to nitrites and then nitrates …….
IMO your best bet would be to add some FULLY cured live rock, if you can get your hands on some as well as good sized daily water changes.
Your pH is fine at 8.3 or 8.4. What pH are you trying to acheive?
The ammonia level you are getting is only part of the picture. Ammonia is dependent on pH and temperature. Most test kits on the market test for total ammonia, which is the combination of highly toxic ammonia molecules and relatively harmless ammonium molecules. Toxic ammonia is a percentage of the total ammonia That percentage is based on the pH and the temperature of the water. So your toxic ammonia is most likely not .5 it is probably lower. Toxic ammonia will be higher in tanks where the temp and pH are higher. If your kit tests for total ammonia, then take the measured amount and multiply that by a value found in a special table. That value is based on your tank temp and pH. The result is the amount of toxic ammonia in the water. The tables with instructions can be found by doing an online search if you want to calculate yout TOXIC ammonia.
To determine if your test kit tests for toxic or total ammonia check the instructions carefully.
So you could lower you tank temp a bit and that will help to lower the toxic ammonia. If you are adding anything to keep your pH at 8.3 to 8.4 I would stop and let your pH be a little lower while you are having this ammonia problem. A pH of 8.0 to 8.2 would be fine for now. I would however not use any additives to lower the ph.