Is there a method for reintroducing a betta into his tank after a partial water change? I ask because I imagine the water will be slightly cooler before the heater has a change to catch up. I've let the water sit out, so it's room temperature, but room temperature in New England these days is a wee bit nippy.
If you're worried about your betta going into shock, just float the cup in the tank and go about it like a normal acclimation. (That's assuming you got your betta in a cup, or have a cup on hand) Slowly adding in some water then letting him go into the tank :) What size tank do you have? Do you use a water conditioner?
With my ten gallon tank, I try and match the water from the faucet and the tank, then condition it, then add it. I don't re-acclimate my bettas. But I suppose if you have a smaller tank than that, the temperature difference would be much more noticeable.
I bought a couple 5 gallon buckets new to help me with water changes. I filled one of them up and I'm letting it sit, treating it w/ dechlorinator and also w/ pH down, because my tap water is very, very high. It's been sitting for several days, which I am hoping will help if the pH down causes the water to freak out. I bought a small critter keeper for him to swim around in while I vac out the water, so it can't float. I was thinking that maybe slowly introducing the new tank water into the critter keeper before putting him back in his tank might help.
Thanks, everybody, this was very helpful. I just wanted to make sure I wasn't missing something critical. I've never actually cleaned a fish tank before, so this first time is going to be an adventure. Do you usually remove everything to vaccuum the gravel or do you leave ornaments and stuff in?