That's one of the things with sick fish, short of viewing an actual smear under a microscope, and knowing exactly what to look for, all most of us can do is take an educated guess. White stringy looking waste, and refusing food is certainly a couple of the early signs of hex, but according to the studies and data currently available (which in the link below actually involved angels) Epsom salt only works if ingested, or if applied via bath at levels that far exceed what any hobbyist would typically use.
http://scholar.lib.vt.edu/theses/available/etd-120399-140825/unrestricted/ANGEL.PDF
Later in the paper it states .........
My guess would be this, in your case your angels had a case of hex/spiro, which you caught in the early stages and the Epsom salt helped the fish shed enough of the parasites for the fishes own immune system to take over. The problem is this will not always happen, especially to a fish that has a compromised immune system. That, and the parasites won't actually be gone, they will simply go back to living off the host fish, but in check, in reasonable numbers that the host fish can deal with. Most parasites don't want to kill their host, they want to keep it alive as that is their food source. Having said that, at the first sign of any real stress, the pathogen will take off again, multiplying out of control and you are back at ground zero again.
I prefer to kill the pathogen, completely, 100%, so that it can never return. Epsom salt have been used for many years in the aquatic world, but baths are not typically recommended as solution for hex/spiro, as in most cases the fish will not recover. If the parasites become systemic, and end up travelling to the blood. muscles, and organs, even ingesting or force feeding Epsom salt may not work, where some of the varies medications such as Metro have proven to still be effective.
I didn't want anyone thinking that they can cure a fish with hex/spiro by simply adding some Epsom salt to their tank. In that situation, most sick fish would die.
It can help for sure, but it's not typically a cure.
HTH
http://scholar.lib.vt.edu/theses/available/etd-120399-140825/unrestricted/ANGEL.PDF
Magnesium sulfate inhibited the growth of the parasites only at high concentrations (70 mg ml-1 or higher) . This study indicates that dimetridazole, metronidazole and mebendazole are the most effective chemotherapeutic agents in vitro at inhibiting the growth of S. vortens.
Later in the paper it states .........
1.4.4: Magnesium Sulfate (Epsom Salt)
Reducing the number of burden organisms by saline purges is an alternative method in the treatment of parasitic infestation, especially from luminal parasites. Saline purges all act in a similar mechanism by which the anions and cations are slowly absorbed from the digestive tract. Magnesium salts frequently used as saline purgatives are Magnesium Sulfate, (Epsom salts), Magnesium Hydroxide, Magnesium Oxide, (milk of magnesia), and Magnesium Citrate, (Jenkins, 1988). They retain or attract water into the intestinal lumen mainly by osmosis, which distends the gut and increases peristalsis, thus producing defecation. Another mode of action of magnesium salts is causing the release of cholecystokinin, which increases peristaltic activity of the intestine (Jenkins, 1988); intraluminal parasites then will be expelled from host. The concentration of saline purgatives should be isotonic such as 6% solution of Epsom salt to get a quick purgative action (Alexander, 1985). In the present study, magnesium sulfate which may be helpful in reducing the number of diplomonads was examined for an efficacy in inhibiting the parasite’s growth.
My guess would be this, in your case your angels had a case of hex/spiro, which you caught in the early stages and the Epsom salt helped the fish shed enough of the parasites for the fishes own immune system to take over. The problem is this will not always happen, especially to a fish that has a compromised immune system. That, and the parasites won't actually be gone, they will simply go back to living off the host fish, but in check, in reasonable numbers that the host fish can deal with. Most parasites don't want to kill their host, they want to keep it alive as that is their food source. Having said that, at the first sign of any real stress, the pathogen will take off again, multiplying out of control and you are back at ground zero again.
I prefer to kill the pathogen, completely, 100%, so that it can never return. Epsom salt have been used for many years in the aquatic world, but baths are not typically recommended as solution for hex/spiro, as in most cases the fish will not recover. If the parasites become systemic, and end up travelling to the blood. muscles, and organs, even ingesting or force feeding Epsom salt may not work, where some of the varies medications such as Metro have proven to still be effective.
I didn't want anyone thinking that they can cure a fish with hex/spiro by simply adding some Epsom salt to their tank. In that situation, most sick fish would die.
It can help for sure, but it's not typically a cure.
HTH