At a loss

(Sorry about my test page, it got wet and I didn’t realize before opening it and ripping it apart🫠) I noticed high alkalinity two days ago, drained most of the water and cleaned the filters, and refilled with good water (I tested it before filling the tank). Otherwise filtration is good, temperature stays between 70°F-75°F, and water is clear. Well, it’s the next day and my water is back to high alkalinity. This is my shrimp tank, I had a few neon tetras that I moved to my other tank that has consistently perfect levels. I got this tank setup for Christmas and everything has been fine up until now, I haven’t changed anything to spark this issue so I have no idea what’s going on or how to fix it. Please help!