Oodinium is the most perilous fish disease with Parosphromenus. The problem is that the spots are very small, much smaller than Ichthyophtirius. Therefore, it is mostly detected too late for being treated properly. In fact, many wild caught fish are infected by the stress of being transferred from one container to the other without being fed properly for weeks. But in the first weeks the infection is very difficult to be seen at all. It needs best lighting to observe the fine powder-like appearance of a stricken individual. Mostly people react too late when the disease has become obvious. Therefore, we had a practice that was used by most ambitious breeders for years: to treat new fish in advance with 2-amino-5-nitrithiazol; but this will not longer work if you are unable to get hold of the fresh (!) substance itself(see below).
In Michael’s description it is not clear to me whether it is a very late and heavy infection with Oodinium or something else; it sounds rather like funghi, but it could nevertheless be heavy and lately observed Oodinium.
In that state it is nearly hopeless to get the fish healed again. The medicines normally sold for combatting Oodinium are mostly effective in very early stages only; they are of no help in intermediate or even late stages. The only efficient medicine we know of is 2-amino-5-nitrothiazol, a yellow power, which was sold as “Hexa-Ex” (by Tetra) or Spirohexol (by JBL) in a pressed solid form. It it becomes brown (after a few months, if not stocked properly in a refrigirator), you can throw it away; it has become ineffective. Since one or two years however they sell it in liquid form which is better to apply, but it is inefficient against Oodinium. So, at present we have no efficient medicine against Oodinium. The only thing we could try is to recognize the disease as early as possible and use salt and higher temperature at once for two weeks.
I am afraid, that this is no cosolation for Michael. I don’t see how his heavily infected fish could be helped for sure. Of course, you should try with salt and higher temperature rather than the usually sold medicines, but the outcome is open, I’m afraid.