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This article will help you: https://www.gardeningknowhow.com/plant-problems/pests/insects/organic-snail-control.htm

Please include some photos, and I will be glad to help you. There could be many reasons for this happening, but seeing where it resides can help me narrow a few things down.

https://www.gardeningknowhow.com/ornamental/water-plants/lotus/how-to-grow-lotus-plant.htm

It will be similar to outdoor care. This will mean keeping the soil saturated, and very bright light. It will, likely, be necessary to use a grow light to help it along through the winter.

This article will help you with the general care requirements of the plant:

https://www.gardeningknowhow.com/ornamental/water-plants/lotus/how-to-grow-lotus-plant.htm

I would remove that since it may provide an entrance for disease or pests. But it should not affect the growth of the plant. Here is more on its care:

https://www.gardeningknowhow.com/ornamental/water-plants/lotus/how-to-grow-lotus-plant.htm

This will entail a little more work on your end, but it isn't something that can't be done. Using potting mix as a filler can work if you thoroughly rinse it first to remove excess fertilizers and chemicals. Layering 6″ of proper aquatic soil on top—with pea gravel or river sand as a cap—can create a suitable rooting zone for your lotus seeds while helping maintain water clarity. However, potting mix is designed for terrestrial use, so it may leach nutrients that could affect water quality. As an alternative, you might consider mixing the potting mix with an inert filler like washed perlite or pumice to minimize organic content, or use it only in non-submerged areas. Regular water testing is advised to ensure the environment remains ideal for your plants.

https://www.gardeningknowhow.com/ornamental/water-plants/lotus/how-to-grow-lotus-plant.htm