The Best Pond Sealant - Beware of Imitators!
Concrete based ponds need the final render sealing to stop the water getting in and lime leaking out. G4 has been long established as the market leader for this task. You need 3 coats of clear G4 when you apply it to a pond. This is a total of 550g per square metre. There is enough sealant in a 5kg tin for 9sqm (eg, a pond of 2m long x 1m wide and 1m deep = 8sqm)
Green water is a problem that many pond keepers have to deal with, especially in the summer months.