Thanks for the replies - I decided to euthanize the fish today. It was obviously not going to make it & I didn't want to prolong the suffering. I'm really at a loss about what happened. I would like to try & figure out what is happening, though, so I'll attempt to answer the questions asked.

The tank has been very stable since the illness outbreak in June/July. At that time, I lost 6 julii corys & 4 glowlight tetras over a period of about a month. I had treated with Furan2 & two rounds of M/MII. Also did a salt treatment prior to that because I was concerned about them possibly having subclinical ich or velvet & didn't want to use ich meds with the corys. Once I saw the bacterial issue arise, I began treatments with the meds mentioned above.

I test my water at least weekly, change at least 50% every Sunday & have not missed any changes. I haven't observed any spikes of ammonia or nitrite & nitrates are consistantly below 10ppm. I use the API liquid reagent tests & the normal pH tests @ 7.6; if I use the high range pH test, it reads 7.4. I do nothing to alter the pH. I use 3mm of Prime when changing water (29 gallon tank).

I've used the Seachem products Flourish Excel, Flourish Trace, & Flourish for several months now. Several weeks ago I began adding the Flourish potasium, nitrogen, iron, & phosphorus. All are dosed according to instructions (amount & frequency). Also use Flourish root tabs for my swords about every 3 months. One of the reason's I'm so religious about the water changes is to avoid any build-up of extra nutrients that I'm adding. I have a CoraLife 6700K 65 Watt PowerCompact light on the tank. No algea issues (crossing fingers!).

No temperature fluctuations, no new ornaments, no new fish, no new plants. The fish food is made by a fish hobbyist & he uses human grade ingredients without fillers, artificial colors, etc. - here is a link to his ingredients page: www.almostnaturaltropicalfishfood.com/ingredients. I've no qualms about the quality of the food. My fish get a 4 different foods on rotating days, along with a pea or two weekly.

The remaining 4 (lonely) tetras in the tank seem to be fine. They are actively swimming & schooling together, no signs of ich, velvet, clamped fins, or any other odd behaviour. I have a new shipment of fish coming in this Friday to increase my tetra school back up to 11, 6 more julii corys, & a honey sunset gourami. Of course, they will go into QT (tank is fully cycled) for at least a month before going into the 29g. I certainly don't want to expose them to anything, hence my concern about sorting this out.

I try my hardest to be a good fish mom! Any suggestions you can give me to put an end to the tank of death would be much appreciated! Thank you for your time.