Liquid test kit, or strips?We have had him 3 months. He was healthy and happy for the first month and a half or so. Then I did a 50% water change and he started acting off.
I have top fin water conditioner and api test kit
No need to let water "sit", you can add the conditioner & fresh water at the same time
Something about the WC affected the fish, though...you didn't forget to add conditioner, correct?
The Top Fin stuff is OK for now, but get some Seachem Prime, or API Tap Water conditioner, and use that
And, a bigger tank is easier to keep water params stable