Experience using kurusi wormer plus

[kendall18]

1 have a 55 gallon tank with 4 3 inch and 1 5 inch discus. Temp 29 no ammonia or nitrite ph 7.5. I noticed one of my discus starting to get quite thin and he and a couple of others had white poop. I live in nz and the only thing I found to treat internal paracites is kurusi wormer plus. I followed the instructions and treated 2 doses 4 days apart. Everyone looks good now apart from the little nod and the big one. Little ones poop seems the have improved to brown but still looks realy week and fins seem to be getting torn but still eating like a pig. Have I left it to late to treat him or could he improve? And the big one has always hid when I'm near so he is still hiding and still has white stringy poop and not rely eating. Any advice would be good