I don’t think that’s an aerial leaf. It should be round. It might be ready to send one up soon. When it does, the submerged leaves should melt off so don’t worry.
Your beautiful bowl has clear water, fish okay, plants growing, etc). The lily is now starting to send up aerial leaves. That will help spur growth as it will now be able to bring oxygen into its soil substrate. Are you sure you want to mess with success? Instead, you could set up a small tank or bowl to tinker with new ideas, buy another lily, and play around with NC clay.
I dunno. I just couldn't keep the vision of @dwalstad 's beautiful summer tubs out of my head, so I followed your advice and set up a separate tank for my red clay experiment.Instead, you could set up a small tank or bowl to tinker with new ideas, buy another lily, and play around with NC clay.