All the lotus seeds that I've grown (not that many) have sunk and started putting out a root within just a few days. I've heard people say that any seeds that float are no longer viable. I've found that to be untrue with many varieties of seed but I think that viable lotus seeds probably do sink. If they don't start growing in about a week they're probably dead.
Karyn

Thanks, Karyn! Well, 36 hours later two of the floaters have now sunk to the bottom... and all five are swelling with water. No sign of roots yet, but I will definitely give them a week before giving up on them!

All seeds were floating at first and eventually sank, however I have one that is floating still but sprouting, we shall see.

Hi. I've raised Lotus from seeds for four Years now. It has been MY expirence that floating seeds are no longer viable. I generally toss the floaters. My first couple of years doing this I tried to keep my floaters thinking they just might survive. But each time the seeds only grew fungus and fouled up the water. Now when I'm growing my lotus I always just toss out the floating seeds as they have NEVER sprouted for me. If you received a package of seeds and they all floated as you stated, I would defiently ask for a replacement pack of seeds from the vender! What kind of lotus are you growing? I've ordered nuciferia seeds and have had venders send lutea seeds in the past so be careful of your venders also they like to swich up seeds sometimes. The nucefieria is the asian lotus and the lutea is the American lotus and there is a difference. Also a difference in the flowers. So get a good vender you can trust that won't send floating seeds and will send you the correct seeds you have ordered. Good luck growing your lotus! Remember to have fun and lotus growing is very rewarding so don't give up! :) happy growing