It’s smart to seal any new pond you’re building, so pond sealer should also be part of your expense list. If you have an existing pond it’s time to consider pond sealer when you realize it loses water faster than usual, especially if the water level drops after you shut off the pond pump. This usually confirms that there’s a leak in the pond liner or even the pond’s foundation. Remember, it’s not always the sun causing more water to evaporate: there could be crack somewhere that needs fixing. You can find a crack by adding a few drops of dye or milk to the water. You’ll see where the molecules travel to because if there’s a crack the pull of the flowing water will guide them towards that opening. Watch the milk or dye closely and you can determine where the cracks are even if they’re not visible to the naked eye.