This is natural. This is okay for the fish except that you cannot see them to see any problems they might have. Test your water once a week. When the water begins to warm up the biosystem will begin to start functioning but will not be fully operational until the good bios are established for the season. You will need to periodically add to or change the water.
Water does evaporate in hot weather and topping off the pond about once a month is normal.
Add dechlorinator to any water from the tap. Chlorine burns the gills of the fish and will kill them. As we pointed out in the paragraph above, having any readings on either test can and often kills fish. We're here to help you. Ponds are as unique as snowflakes.