First off, sorry if this is a stupid question. I'm sort of a plant noob and this is my first tank since I was a kid. I know my tank isn't super set up for plants, but I figured I'd get better advice on here than the general aquarium sub. Don't laugh. :P

I noticed last night that my amazon sword is turning yellow on several of its leaves, mostly near the edges but on at least one leaf it's mottled all the way through. It's the only plant in my tank that doesn't seem to be flourishing.

It's the closest plant to the heater, if that means anything.

5 gallon, 12.3 inches tall.

LED lights, the default that comes with the Fluval Chi.

Don't believe I have a ballast

Lights are generally off from midnight to like 8 or 9 am.

Default Fluval Chi filter, no idea on GPH. (If anyone knows I'd appreciate the info)

Substrate is black microgravel

No added CO2

No ferts

Tank is stocked with one baby betta, and planted with java fern, duckweed, amazon sword, cryptocoryne, bacopa, dwarf hairgrass and a moss ball.