Hendrik, my little Baby Doll lotus was in a pot about 10in. across, and 8in deep. The lotus do need a fair amount of fertilizer to grow and bloom well. I let it die off because it didn't get enough sun in my pond, which is in the entry to our house and gets a max of about 3 hours of sun per day. So, as I said, in June (highest sun here) it got enough, but even though the leaves are lovely, only one month of bloom was a disappointment.
Jonna,
with Becky. Not sure that water lettuce will die off in the heat, it grows like crazy here almost year 'round. Cold weather knocks it down, but it comes back. I'd roust it out for compost asap! Very invasive.