A few days ago this white patch appeared on one of my Dwarf Gouramis. I've tried dosing some Seachem ParaGuard into the water, but it doesn't appear to have helped at the moment.
Any ideas on how to treat?
All the other fish are okay and the water checks out fine. The tank has been running for a few months now. I think the other Gourami in the tank has possibly been bullying this one but I don't have a spare tank at the moment to isolate him.
Hi This isn't white spot (which is multiple small spots that look as though the fish has been sprinkled with salt). It's a serious bacterial infection. You can treat with Esha 2000, but I fear the fish has the Dwarf Gourami iridovirus which presents with lesions like this. If that's the case, there's no cure and while Esha 2000 may help with the sore in the short term, long term the fish will become much sicker and eventually die. Sorry to bear bad news, but the majority of farm-bred Dwarf Gouramis are infected with this and most don't last more than a few months to a year after purchase.
The virus is highly contagious and the other DG is likely to already be infected. It is of minimal risk to other species. Any medication that can treat the symptoms (as nothing can actually cure this) is risky for snails so it would be best to remove them to a container of water while treating. Do a large water change at the end of treatment and run carbon in the filter for 48 hours before putting the snails back in the tank. The other option is to euthanise the fish - he is not going to get better, just maybe have his symptoms suppressed short term. Arguably euthanasia is kinder. You can put him to sleep with an overdose of Aquased, a fish anaesthetic, and he will go peacefully.