I understand, but if you want to do this right you can't rush through it.
Clear Diamond, from what I read on their website, although a sealant for external concrete, does not mention suitable for constantly wet or submerged conditions. The use of these types of sealers/coatings invariable will lead to an earlier failure in the seal integrity than those products formulated for submerged conditions.
Marine sealants/coatings are formulated expressly for these conditions.
The photos below show a concrete pond renovation that I did a few years ago using just such a marine sealant (Urethane in this case).