Help please. BN with fluid filled sacks on belly and gills

Hi

I hope someone can help me as I'm at a loss of what to do next. I've kept BN Ancistrus for over 10 years and I have never seen this before. (sorry not allowed to add photo yet as newbie pm me if you want to see the image)

History:
6 month old Ancistrus breed myself. Broke his fin 4 weeks ago tussling with my adult male I think. He seemed fine and the fin had started to grow back nicely (as seen in pic) 1 week ago a swelling appeared under his fin. I have isolated him and treated for internal infection with Myxazin plus added Epsom salt. He has now developed fluid filled sacks under his belly, and around his gills which are turning slightly red and he's also developed a bit of pop eye. I'm thinking this has turned into septicaemia or could it be something else? I am thinking of taking him out to directly apply the Myxazin to his body as a last ditch effort to save him but I'm not sure if this will just finish him off.

Has anyone seen this sort of thing before? Any clue what has caused it (other then the broken fin/infection)? Any ideas on what else I can do to save him? Should I admit defeat and deal with him humanely?

Tank & Fish he was in with
64 litre tank
1 adult ancistrus & 3 juveniles 6 months old (lost my breeding female 3 months ago aged 5ish)
4 Cardinal tetras
3 Swordtails
Water perimeters tested last week were:
Nitrate = 25 mg/l
Nitrite = 0 mg/l
Ammonia = 0 mg/l
PH = ~7.5
Temp 26c

Quarantine tank 45 litre has gravel, plants & rocks to hide under (normally my breeding tank)

Water perimeters tested today are:
Nitrate = 10 mg/l
Nitrite = 0 mg/l
Ammonia = 0 mg/l
PH = 7.5
Temp 26.5c
General maintenance :water change weekly with gravel clean every 2 weeks

photo is my avatar for now

I've not seen anything like that before, on any fish.

I'd keep going with the Myxazin and salt treatments. As a last ditch effort I'd lance the 'blister' immediately after dosing with Myxazin

Are you sure they're fluid filled? Please, try upload better picture on photobucket. It kinda looks like caro luxurians, but no idea how to treat it in case of fish.

Thanks guys.

He's still hanging in there but no major improvement he did eat something today which he hasn't done for days. They are defiantly fluid filled almost like mini balloons.

Still can't add pictures will have to wait another 5 days sorry.

Thanks