If you know of a decidious woodland, find a spot on the lowland slope where centuries of soil have developed high fertility, dig down a foot you will find ideal loam for potting waterlilies, lotus, aquatic plants.
It takes a pond about a month to deplete fertility levels in the growing season, figure a way to insert slow release fertilisers to pep up growing rates further
Wrap a couple of cubic inches of any standard fertiliser in cling film, seal it, poke a couple of pin holes to slow release... to make your own super dooper plant 'pills' to insert beneath your favourite pond plants
This will double and triple blooms...
With a dash of dried cows blood added, this will make the bloom colour tones really pop. They like the extra iron content.