It's great you found Kana!

No... you don't have to change out any of the water daily. Kana becomes inert after 48hrs. You can refresh the tank, say mid-week, with a partial waterchange between a full weekly waterchange. Just be sure that when you do either partials or full waterchanges, that you do it right before it's time to administer the next dose so you're not removing the meds too early. It's important to dose the meds at approximately the same time daily so he's not without any active antibiotic in the water.

Also keep in mind it is very common to do 2 full rounds of antibiotics b/c we often don't see any real improvement till near the end of round 1... and stopping too early will enable the bacteria to regain a hold. 2 rounds is perfectly safe. However, you might consider stopping the meds before proceeding to round 2 if there was no improvement noted at all by the end of round 1. We can visit that together with your updates, k?

Are you using anything to oxygenate the water? Perhaps an airstone, bubbler or empty filter?

Michele