BIG, fast change in pH

[fishwatcher]

Just wondering, 2 days ago I had a sick neon. I medicated it with a parasite medication. I tested my water just now (after doing a 10% water change) and noticed that the pH has risen quite a bit... it normally is about 6.8, now it is 7.2. Could the meds have done this? I'm stumped, as that is the only change that has occurred. I am worried it might crash and kill everything. What causes pH to rise like that???

 

[Fiori]

If you noticed it after a water change, my inclination would be to check the pH of the water as it comes out your tap.

 

[fishwatcher]

It is 6.4 out of the tap. That's what has me concerned...

 

[fishwatcher]

Any other ideas?? I just don't want the pH to crash and kill all the fish.