Hey Scotty!
I have a 2000 Honda Accord lx 2.3L 4 cylinder and ive been noticing im losing alot of coolant. I tried the UV dye method but cant find anything. All the hoses and water pump seem fine. Also I've been hearing what sounds like water swishing around from the inside. My temperature gauge doesn't rise abnormally but i just have to put more coolant in the reservoir after a while and hear that noise from the cabin. Could this be an issue with the heater core? Greatly appreciate your help.

heater cores leak, then coolant will leak into the dash or under the car at the ac evap drain hose. Most likely your head gasket is blowing, do this video test https://www.youtube.com/watch?v=QA7KVQq9vKA&t=61s