Sick/injured Apisto Cacatuoides

I've had these Apistos for about a month now... I have a pair in a 10 gallon aquarium (pH=7.0, no ammonia or nitrite, 77F, 10-20% water change daily, fed frozen daphnia and bloodworms). 5 or 6 days ago I noticed what looked like an injury just behind the left eye of my female (red arrow)... It's been swelling slightly more each day, and today a second pimple like swelling became apparent just behind the first one (blue arrow) - this is exactly what the first one looked like 5 days ago. For this reason, I think the problem is something other than an injury. I added some salt to the water (2-3 tbsp) a few days ago and today, on the advice of a guy at my LFS, began filtering the tank through peat and began treating with Erythromycin. The fish is still active and feeding well, though I wonder how much longer this will last.. any ideas are greatly appreciated.



-Andy

Is the pimple ulcerating the skin away making a hole.
Does the pimple have any puss coming out of it.
Is the fish in a hospital tank as antibiotics can wipe all the beneifical bacteria out if the filter.
Are the pimples white on the edges and pink in the centre.
Does the pimple look like a caulifower or a cluster of eggs.