When I install a filter in my kitchen, the reading in the outlet goes down, but the reading in another outlet goes up. Why is this?

This can be caused by improper wiring in your home. Sometimes multiple circuits share the same neutral return, causing an imbalance. Under these conditions you could have the reading in an outlet go up. Some other things can cause this too. Try installing more filters at the problem site and this usually solves things. Look for the best combination of filters in both outlets to reduce the readings everywhere as low as possible.