Fin rot fungus?

[Crg12]

I recently paired up some juvenile dark knight rams and the female seem to have had her dorsal ray nipped. At first i thought it would just heal with just water changes. However, it seems to now have advance and looks like fungus is on there. I’ve been treating it with erythromycin. It’s a breeding setup, no tank mates besides her pair, he is healthy. She has no progressed to just sitting at the bottom breathing faster. Any advice or insights? Pictures below.

 

[Andy Sager]

I have a few questions:
1) How long have you been using the erythromycin?
2) What is the water chemistry ( primarily the Ph)?
3) What temperature are you keeping the fish at?

The answer to these can determine the next step.

 

[Crg12]

I have a few questions:
1) How long have you been using the erythromycin?
2) What is the water chemistry ( primarily the Ph)?
3) What temperature are you keeping the fish at?

The answer to these can determine the next step.

She unfortunately passed but I’ve used erythromycin two days before. pH was at 6.8, temperature at 30 Celsius. I don’t know what it was because the pair she was with is healthy.

 

[Andy Sager]

She unfortunately passed but I’ve used erythromycin two days before. pH was at 6.8, temperature at 30 Celsius. I don’t know what it was because the pair she was with is healthy.

Sorry to hear. Sadly, Erythromycin is a 10 day treatment so 2 days was not long enough for it to really do any good. Combine that with the Ph being too low for maximum effectiveness for the drug.
I suggest you read the following: https://www.americanaquariumproducts.com/AquariumMedication2.html#erythromycin

For what it's worth, I would have gone with either Kanamycin( Kanaplex) or Nitrofurazone for this fish. These are more effective broad spectrum drugs for most common freshwater diseases. More advanced diseases may require more specific medication.

Hope this helps.