well .... let me start by pointing out some important issues with your tanks:
Gobioides broussonetti - the dragon or violet goby grows to a foot and is a brackish water fish. none of your other fish are brackish and therefor, this fish doesn't belong in the same tank with them.
Brachygobius xanthozona - bumblebee goby is a brackish water fish and certainly doesn't belong in the same tank as discus, which prefers a soft, low mineral content environment.
Osteoglossum bicirrhosum - arowana, grows to 2 feet and if well maintained, can grow to 4 feet. keeping this fish in a 29 gallon tank just makes no sense. moreover, it will need a 6 foot tank when it grows to maturity.
Macrognathus aculeatus - striped peacock eel, while the smallest of the tire tracks, still grows to over a foot and need a much larger tank than you've got him in.
the fish you currently have in your tanks are going to outgrow them sooner rather than later and you're going to have serious problems. fish maintained in tanks which are too small or in conditions which are too crowded, develop severe stress syndrome. these fish do not exhibit proper color, do not develop proper fin form, do not exhibit proper metabolic development, do not exhibit normal behaviour, do not develop proper musculature, do not develop properly functioning organ systems and as a result, slowly lose their inherant resistance to disease. this results in a significantly shortened lifespan and along the way, lots of diseases for which the poorly conditioned fish is a good target.
i don't know to what fish you refer to as an LEI but it sounds like it "may" have a viral disease known as Lymphocystis. this diseasse infects cells and causes them to become megaloblastic, i.e larger than normal.
this disease used to be considered untreatable as most viral infections. recent research however, has shown that neutral Acriflavine "may" be effective in treating this disease. "Aquarium Products" makes a product called "Lymphocystis Cure" which contains Acriflavine as its active ingredient. if you cannot get this product, try and find neutral Acriflavine in raw form. failing that, try and find a product containing it ... (Jungles Ich Guard for example). the latter may or may not work due to the relatively lower dose of Acriflavine it contains, but it's worth a try.
treating in a well aerated hospital tank - Bathe the fish 3-5 hours in iso-thermic iso-pH water according to label instructions for the Aquarium Products and replace the fish in its main tank. Re-bathe again in five days when, if the product is working, you will already be seeing a reduction in lesion mass. Regrowth has not been seen after complete clearance.
note, Acriflavine will not work on other granulomata or cancers. note too, that as a virus, Lymphocystis is rarely fatal and may run it's own course and disappear on its own.