G4 Sealer is the most efficient tool for accomplishing this.
It is just painted directly over the hardened concrete.
You can choose between clear (dries translucent) and black.
In order to make waterfalls, statues, and other concrete objects safe for your pond, you can also cover them with G4.
For concrete ponds, G4 Pond Sealant is a one-component deep-bonding polyurethane sealant.
Gives all shapes a crisp finish quickly and easily.
Keeping lime out, friendly to fish
Useful in cold temperatures
Useful with anti-crack fibre