Internal Discus Parasite/Bacterial infection - what to treat with first

[KrisR]

Hi guys,
My tank is located in Vanuatu. I have a 8x2.5x2.5ft planted tank, with sump (altogether about 1400L). Almost 100% of the fish were added at the same time, about 4 months ago. Importing the fish from Australia was a long and arduous process which took about 18 months of paperwork to organise. Not to mention great expense. Which makes it all the worse that my discus are slowly wasting away and dying with no external signs!

Tank specifics:
Mixed community tank heavily planted, injected with Co2 and fertilized with diy ferts to AI spec. Community includes discus, glass cats, cardinals, guppies, mollies and platties, corys, kuhli loaches, some local shrimp although I never see them. Ph around 7.5 GH and Kh both around 5. To achieve this I mix bore water and rainwater 50/50. I change 50% of the water weekly. Substrate is mineralized garden soil topped with sand.

Discus illness specifics:
I have kept discus successfully before. In Perth I had a 8x2x2 with a group of 16 discus which I kept with minimal issues from 2005-2009. These current discus were supplied by Bay fish in Queensland. When they arrived I was amazed at the quality of the discus - compared with my previous ones they were much friendlier, eating beef heart recipe from my hands on the first day, and swimming right up against the front glass without hiding when people approached the tank. Over a period of months, several of the discus became withdrawn, not wanting to feed with the others and hiding out in the upper extremities of the tank. Based on previous experiences, along with the fact that only the discus were affected (all other tank inhabitants are thriving, breeding, feeding heavily etc) I put it down to some community behavior and aggression. Over the months I have lost nearly a third of the original 25 5cm discus I received. The losses are accelerating, with two dying in the last week. I am today removing all the discus from the main tank into a 50 gallon 3ft tank for treatment.

Syptoms:
The affected discus are lethargic, not feeding and losing colour (although not turning black). They aren't rapid breathing, showing any visible white spot, fungus, fin rot or anything else I can identify externally.

Here in Vanuatu, there is no LFS - so access to aquarium specific meds is limited. I have access to Sykes Big L (Levamisole), Aristopet Praziqantel tablets with Pyrantel and Oxantel (dog worming tabs), Metronidazole in a liquid form and a small amount of Nitrofurazone powder. I am planning to hit with the pyrantel tabs first, dosing the whole tank, then the levamisole a week later, then the metro and the nitrofurazone as a last resort if they haven't improved with the first steps... Can anyone suggest any changes to this plan?

Would you consider the Oxantel and Pyrantel in the Prazi tablets safe to add into the aquarium? The tablets constitution is as follows: 100mg Praziqunatel, 1084mg Oxantel Embonate and 286mg of Pyrantel Embonate.