I can actually answer that fresh, see below from Krylon
Thank you for contacting Krylon.
Unfortunately, we do not recommend any of our products to be applied below the water line. None of our products are immersion-rated or waterproof. Our products may last for a time under water, but there is no guarantee as to how long the will hold up.
Additionally, we have nothing that is FDA approved, which is important in terms of ingestion. Our products may harm the aquarium life.*
I wish you the best of success with your search for a compatible product. Please let me know if you have additional questions.
Krylon Product Support