Tangs not meant to be or what???

[smitas5]

2 months ago lost a very nice clown tang only 3-4 weeks in without any signs og sickness.
Today lost naso tang only 2-3 weeks in too. He did have some spots on his fins. Maybe 4-5 in total, feeding like crazy, did not see any issues with him, but had to treat the tank for second time for fluke parasite with prazipro, found naso dead next day... Is it the species or me?.. Too afraid to buy another tang now.
Other fish in the tank. Yellow boxfish ( a bit ichy), six line wrasse, blue cheek trigger, 2 true percula clowns, some other red wrasse in 120G
Water is tested couple times a month.


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