To me, this looks like some kind of fertilizer burn.
What kind of fertilizer did you use, and how much?
What kind of potting soil?
I hope there isn't any straight cow manure in those pots.
Also, once you plant them in the spring, it is absolutely NOT necessary, if you use my recipe, to add extra fertilizer at all for the entire season.
A lot of people kill their lotus by fertilizing on some kind of schedule, such as once a month or every 3 weeks, just because they read it online somewhere.
I am talking from experience here, cuz I used to kill ALL my lotus by fertilizing on a schedule with spikes and/or tablets.
Did this for almost 5 years until I decided to try something different, to mimic Mother Nature as closely as possible.
That's why I do not use tomato spikes or any kind of spike or tablet fertilizer. They tend to dissolve WAYYYY to quickly and that is when fertilizer burn happens, and plants die.
And from what I see all over all the pond forums, is that people use WAYYY too many spikes when they jam 'em into the pots each month.
People tend to overkill (No pun intended) when it comes to fertilizer.
That is why I came up with my recipe of slow, time and temp released nutrition, using Osmocote at the bottom of the pot so it slowly leaches up and through the roots,
and because there are the least temperature swings at the bottom of the pot, so the fertilizer doesn't get released all at once, or too quickly.
I believe in fertilizing only when the plant is showing signs of malnutrition. I am not advising waiting until the plant is nearly starved to death.
What I am saying is that if you are outside looking at your ponds and plants every day, keep a close eye on all of them. Watch for signs of stress, overfertilization, or malnutrition such as the yellowing of leaves and/or the decline of blooms. Usually my lotus and water lilies starts showing signs of malnutrition so late in the season, I do nothing because it's late fall and they will be going dormant within weeks anyway.
If you don't know what is wrong with your plant, do NOT add fertilizer 'just for good measure'!
Do what Joejoe did, and post pix and ask questions here before doing anything.
