I cannot advice dosage but from what i understand from my dad, isolate the sick dicus and treat it by itself in a seperate tank. add salt, increase temp, dose white spot treatment, etc.
caution - get a reasonably sized plastic tank for the treatment. my dad notice that if kept in a small tank, it dies easily.
disclaimer - I myself is not rearing dicus, buy have observe my dad who is keep them for years.
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