I'm out and about, took a friend to the doctor, and I'm on my iPhone. I'm terrible at texting, so I'll be brief....ooops... Gotta go, lol, be back later.
With a gazillion things going on here as I was posting the above, I left out that the times I have used the above technique, (in bold text), have been when I'm treating a fish that I feel may possibly have impaired kidney function.....
Another option that requires more effort is to slightly reduce the daily dosages that you add to the tank water each day. That is a method that is the method that sherryazure has used on occasions that she treated for Columnaris.
A few here on AC will say that just follow the directions and don't do water changes, but I and many others are concerned that water conditions stay pristine in the tank in which you are treating a sick fish.
Many here agree, and I spoke with several aquaria drug company/technical reps that also say this, that the antibiotic breaks down in the water column after several hours and is unavailable then, so big water changes every day with fresh dosing is fine.
The drug/technical reps I spoke with say the main concern is that the hobbiest won't do big enough water changes to remove residual components each day.
I like doing huge water changes and dosing each day, and I do try to reduce the dose very slightly each day to compensate, but that's tough in a smaller tank. I use a 5 gallon hospital, and though I don't have a chemists/pharmacists scale to weigh such small amounts, I use my eyes to get approximates.
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