Since last posting I have been working very hard on the TDS of our water and any possible contaminants.

I have purchased a 200 litre holding tank that I fill directly from our rainwater system then I run activated carbon in the filter overnight at 1200lph.

I then remove the carbon and add Kent RO right to get the TDS to approx ppm (it changes each time but it is around that). I then aerate, heat and mix with filter head only. That too runs overnight and the next morning I can do 50% water change on my QT tank about 3 times before I refill always making sure that the TDS does not need a little fine tuning.
What does all this do for me?
I can bring home any discus and place it in my tanks and they LIVE !!!!!
No panting to death, no osmotic shock, I have purchased 4 new discus in the last week, 2 adults and 2 juvies and ALL is good.
What a relief!

That's good news

What have you found is the right TDS/GH/KH/PH for your discus?

Well 100ppm-200ppm TDS is fine just so long as there is no more than a difference of 50ppm.

The problem I finally found out is that my water is too pure almost like RO water. Mine is 12-16ppm - RO 0ppm. Fish just cannot live in it at least not the ones I want to keep. As soon as I raised the TDS to 100ppm mine are happy and healthy. Finally an answer. It is so good to know and easy to treat.

ah yes, another australian using rain water

I don't know of any fish that will live in such purified water. RO Right has a mix of all the required minerals for discus. Glad you've got it sorted, the fish look good too

Bit of an update.
Since last posting I have been getting plenty of spawning happening, really good to see. Haven't separated any of them yet into breeding tanks I would like to see them grow more first.
I also have 6 new juvies that I am raising up and finally they have started to eat, they can be very fussy these discus.
So now I have a 4 tanks 3ft for juvies, 4ft for juvies, 6ft for the grown juvies and a 4x2x2ft as the display tank in the lounge. MTS has really taken a good bite off me!

Cheers hope everyone here is well and happy fishkeeping!

PS Eagle - liked you tank, you got my vote!