Just to toss out the question, or "Questions".

Q: What is the most popular OTC antibiotic for fish ?

A: Erythromycin

How many days does it take Erythromycin to reach a Saturated Therapeutic Level ?

A: 10 days

What is the treatment regimen once that level is attained ?

A: 3 days

Q: What Does 10 + 3 = in your part of the world ?

A: I get 13 days here...

Now the $1,000,000,000 Question

Why do 99.9% of those Erythromycin remedies commonly sold OTC Clearly call out 7 days treatment ?

Not to worry conventional "human" medicine commonly does the very same thing ! LOL. God Help Us All !