My syngonium leaves have been turning brown around the edges and I have no idea why. Any ideas?

How do you decide when to water and how much do you give it?

When the top inch is dry to touch, I give it two cups of water.

Does the pot have drainage holes? Why two cups? You need to water the plant thoroughly so that water flows out of the drainage holes. Put it on a saucer or in the sink. Pour away any water collected after 5 minutes or so then don't water again until the top couple of inches of compost feels dry. Watering this way also pulls air through the compost.

I think you are letting it get dry too deep into the pot. It is in a small pot so water it, as Sue has described, as soon as the top half-inch of soil feels dry.

The pot has drainage holes, yes. Two cups are about enough to water it thoroughly. I am watering it just the way you described.

It's an 8-inch pot; it just looks smaller in the photo because I suck at taking photos with my phone, sorry.

It may not seem significant, but the difference between the top inch and the top half-inch of soil drying is significant enough to cause some leaf discoloration.

(Your photography is fine!)

Thank you; I will water it more diligently.