The problem with trying to perform a profound water conditions change - such as reducing / increasing the pH or temperature hugely in response to a sudden crisis - is that a sudden big change shocks the fish very badly and either kills them outright or leaves them much more prone to diseases afterwards due to stress.
The key therefore is to do it veeeerrry sloooooowwwly, so they can adjust gradually to the new chemistry. But sometimes it simply isn't possible to pour new water in slowly enough to achieve this safe adjustment, especially in a very small tank which doesn't really have any dilution capability. And also your arms soon start to ache from holding the bucket!
So... air line tubing siphon! Place a bucket of the new water next to the tank and use air line tubing as a siphon to run the new adjusted water into the tank. The air line tubing has such a tiny diameter that it only trickles water in a minute little dribble. (about 10 mins to replace 1 gallon). This is such a slow change that the fish aren't stressed at all, and you can just leave the siphon to do its job while you go and do something else. You do need to weight the airline down in the bucket though as it is so light it floats and the siphon action is lost (I used a glass paperweight for this ). Also, clip the end in the tank to the side using a veggie clip or similar to make sure it doesn't slip out of the tank and start trickling water over the carpet when you aren't looking!
This 'steady trickle' method also works very well for acclimatising new fish to your water conditions without having to pour hideous disease-ridden pet store water into your tank. (Simply run the process in reverse, i.e. air line-siphon water from your tank into a separate container holding the new fish. After 15-20 mins they will be fully acclimated to the new water conditions. Then simply net them out and place in the tank, throwing away the water they came in).
In case you're wondering, I have used this method myself to alter pH from a sudden and phenomenally dangerous 8.8 down to 6.8 in a 5 gallon tank with a betta and neons in it. The fish showed no signs of distress or discomfort whatsoever.