Since that cardinal died, I only have cardinals with very mild cases now.
I've not done any water changes since I started medicating and although I've not tested, I'd imagine my nitrate levels are building up a bit now. Is it okay to do a big water change tomorrow, or should I wait until the problem is completely gone?
Checked the manual for your fluval 205 external filter, there are 2 bags of carbon in the bottom of the filter. Carbon stops your meds working.