qichai

1. Gill Flukes (Formalin or Condys Crystals) 2.Internal parasites (Metronidazole) Use them with care.

0.3 % is very comfortble for fish, the reason behind this is called osmoregulation.

Yes I have been using tonic for 15 years.

Yes. When fish breed some of them are very stressed. 0.3% of salt water would help them to settle. or some VB.

Try 0.3 % of sea salt in the water and rise temp to 34 degrees for 3-4 days.

30 degree is not right for breeding discus. Around 27 would be better. If they are a breeding pair and had bred about 10 times it will take a while to lay eggs again. there are some ways to make them breed, like after you do 3 days normal water change, do a 80% or 90% water change, and lower down the temp from 27 to 25 and then back to 27 slowly.