Question about planted aquarium and fishless cycling

Is the female guppy chasing the male? Are you sure it's a female? Usually it is the male chasing the female.

Power filter such as Aquaclear should produce enough surface water movement if the water drops a good distance before hitting the surface.

The water temperature is a little low in my opinion. I'd have it set at no less than 76F (I prefer 78~80F), but I doubt it is the main cause of the deaths.

Sometimes even when you do everything right, fish might still die due to they are weak (low quality fish) to begin with. Just make sure you still do everything right, and things will be stabilized after a while. By the way, where did you buy your fish from?