Hi David,
Don't call me Sifu....I have a name and is Andrew..he!he!he!
And Lee, minor overlook is o.k.
Even in forums, I do make mistakes too......wanted to type 'wouldn't' but too fast and typed 'would'.......bad advise...might have killed somebody else discus..hm...
Anyway, 200gm to 200 litre tank is 1ppt and 50% WC redose with 100gm is still 1 ppt. This dose is safe in long term as have been mentioned discus too have at least 1ppt of salt in their spleen.
But then again, what is the purpose? So, I think there is no necessity even though not harmful.
When your discus is sick, we assume that there are wounds whether big or small...and this may result in dehydration thus salt of 1 ppt is important as part of a 'holistic treatment programme'.
AS to your biological filtration system, it should be at least one fifth of the total culture water (tank water space with discus). So, if you have 100 litre of water in your tank, 20 litre is for bio-filtration and 80 litre with discus....and nos. of discus of 4 inches or 100mm size allowed should not be more than 6 (my opinion). If it is flow-through system, you can put more...
Try not to feed worms whether live or frozen..this is my opinion. Let me tell you one thing...
If you use municipal water (treated with anti-chlorine)
Treat your discus to rid of pathogens before you introduce to the system
Maintain temperature between 25 to 28C
Feed only beefheart or processed food 3 to 5 times daily
Make frequent water change
Don't cross contaminate
Individual tank with individual nets and equipments
No live nor frozen freshwater animals as feed
If live feed is preferred, use artemia.
Your discus hobby will be trouble free!!!!
If your system is running well, you should have 0 ammonia and 0 nitrite....check your system.
If you are using bioflitration system, do not adjust pH below 6.6. Between 6.9 to 6.1 pH, the efficiency of nutrifying bacteria drops as they are stressed. Put your pH to 6 and below, they cannot proliferate and will die off...so your system will break down.
Best to put pH for biological flitration system at 7 to 7.5....this is the range they are active.
Hope I am not talking too much
Take care,
Andrew