So I recently purchased a betta (it will be 1 week tomorrow). I set up a 2.5 gallon tank with gravel, a decoration with hiding spots, a java fern, and a heater. The first day he seemed to do ok and was exploring the tank. The next day I started to notice a feathery growth on his dorsal fin. The following day, it was bigger and he was acting more lethargic. I went out and got some Pimafix thinking it was a fungus but this seemed to make him even more lethargic so I did a complete water change as he was barely moving. The feathery thing on his fin came off in about an hours time though. The water changed seemed to perk him up a bit but I still had not seen him since I brought him home, almost 5 days ago. I ran out to the pet store again and they told me to treat with Bettafix since the feathery fungus was gone. The instruction for this says to add the corresponding amount to the appropriate size tank (so about 5mL for me) daily until a water change in 7 days. My question is that since my tank is so new, should I do a water change sooner than 7 days to avoid build up of nitrogenous wastes even though the medication says to do otherwise? He looks much better and I actually saw him eat for the first time today so that is encouraging. Thanks for all the help!