Sick Discus

Ok this is the situation.
I had 6 discus, four large and two small.
One day last week they all looked out of sorts, very dark in colour, some fins clamped to sides. Straight away I thought, great, worms or flukes. Treated the whole tank with flubenol (well, a clone of it). Straight away it seemd to do the trick, and most of the Discus perked up, except the biggest of them. This is the king of the tank, bullied the hell out of everything else. It stayed relatively dark and hiding in the corner etc. Did a massive water change, about 100l (Rio 240). Tested water.
Amm = 0, N02 = 0, no3 = 40-80, ph = 7.0
Now my nitrates are always high, in all my tanks and my tap water too.
I'll check it again tonight. I find the test for nitrate difficult and cumbersome.
However, dip tests have a similar reading.
Back to the Discus.

They all coloured up but remained stressed.
Then the smallest one seemed to contract finrot.
I treated the whole tank but it was too late for this guy.
I was away from the house for a day and it acted fast.
There are some very slight signs of finrot on the others.
The rest of the Discus look resonably healty except some stress bars, except the biggest one, he looks a little thin and has stayed dull brown, occasionally colouring up. All are eating fine.
So I did a 50l water change last night, tested the water (same readings - didnt do the nitrate one). I put in some new clown loaches yesterday too and treated the whole tank for whitespot as a precaution. Noticed quite a few fish were breathing rapidly, cories, tetrae, a pleco.

Holger recommended I treat with a dewormer, which I have ordered and am waiting on delivery.
Has anyone got any suggestions?

Didi,

Haven't a clue when it comes to your Discus problem, A de-wormer is probably the best course of action for the time-being.

Just be sure to keep the water aerated with the whitespot treatment, no doubt this is why your fish are gasping. It removes a lot of oxygen from the water.

Thanks for that Peter, I think you or Deeco told me this the last time I had to use it.
I have aeration set to max, the tank is full of bubbles.
Fluval 4+ is a great filter. Adjustable, easy to clean. Brilliant.

Besides the Flubenol what other medicaion did you use?? I Know you did a water change, but did you run carbon for 24 hours to mop up?? don't medicate to close let one clear and waite a day or so before using another. unless they are compatible meds!!!
Stress bars are what they say, DISCUS do not tolerate Nitrate, Heavy airation will drive off any Co2 and will RAISE the Ph.
Waite until you get the dewormer, if you had watched the post you would have seen I have a stock of dewormer in. Keep an eye on the big one, I.M.E once they go Black they tend to start headstanding, Not agood sign. Keep me posted and make the NITRATE a must test first & formost.
Russ

OK, so they are all looking much better today.
I will test for nitrates again tomorrow and report then.