Your QT comments and saying that you were attentive about that led me in the direction of HLLE, environment, and nutrition. Parasites, and most other diseases will be picked up in QT before fish get to the display. The erosion along the lateral line of the hippo is the pattern of HLLE, but HLLE can also develop anywhere on the fish's body. It's common for fish suffering from HLLE to also contract secondary infections, such as bacteria and fungus, in areas where the HLLE appears because those areas are obviously compromised. Additionally, none of the treatments you've mentioned have done any good. Another indicator that the problem is not really parasites.
All I can tell you is that brine shrimp should be off the table as a mainstay in fish diet. It offers little nutritional value. Occasional feedings (because fish like it and gobble it up) offered as a treat would be my only suggestion with that. Any food can be made smaller. If you can not get a variety of quality frozen foods sold in the hobby that you can get at most pet shops selling fish, then I would suggest making your own food. That will entail getting a variety of what is offered at the grocery store fresh seafood counter, or wherever you get fresh fish food. Use a small food processor ($15) which you can also get at the local grocery store, or Walmart and mix. Roll out the mixture into a square, about 1/2" high, wrap/ziplock, freeze. When you are ready to feed your fish you can cut off a bit as needed, defrost in a cup of salt water for a couple of mins, then in the tank it goes. This does not need to be large quantities of foods that are expensive. A few uncooked marine shrimp, mussels, clams, etc. You can even find some decent frozen at the grocery store but that can not be precooked and should not be seasoned whatsoever. I never much used dried fish foods, except for algae, but others here may have some good suggestions for you about that. (Bold that to see if others may pick up on this and make suggestions.) Quality dry foods will give you the advantage of getting good foods via internet purchase. I would make food a priority along with the selcon or zoecon.
As for water mix, I'd suggest that you not use the airstone. You won't get a good enough mix which could result in undissolved salt getting into your aquaria as well as inaccurate test results for pH and salinity. Get a small powerhead, mix for at least 24 hrs, 48 is better, then test salinity and pH. Are you using a refractometer to test salinity/specific gravity? I'd recommend that highly. Other methods not so accurate.
Leave clowns if you feel more comfortable for now at least.