I started Sacred Lotus from seed. The leaves emerged green but turned pinkish purple after a few days and not in a good way. I move them out of the water garden and into the greenhouse where i could monitor the temperature. Someone said to keep the water at 80 degrees and the nights have been rather cool. The American lotus growing at the lake are in full sun. Another person said the red and pink flowering lotus can't handle direct sun but i thought lotus needed full sun. The greenhouse light is filtered. The leaves are emerging a lighter shade of green and so far they haven't turned colors. I have them in individual pots with heavy soil topped with aquatic gravel. I gave them a half pellet of aquatic fertilizer. What's the problem, the sun or the water temperature? In this photo the leaves are just starting to turn colors. The only other thing in the water was mosquito tabs and water clarifier.
Mosquito tabs won't hurt your plants...check the water clarifier to see what's in it. If it's just barley, that's fine...but if it has any type of algaecide in it, or copper, that will kill plants. I also would watch the bubbler you have. The tops of the leaves MUST stay dry, in order to float and feed the root system (yes full sun is best!) If you get droplets of water, it starts to rot the leaves by choking out their only source of oxygen.