What kind of lotus are they? What kind of soil did you use?

They both came from the nursery so Im not totally sure on the type of soil. The larger one is a Holy Fire Red. Not sure on the smaller one.

Moving plants from a shady spot to somewhere in full sun isn't good. You should slowly acclimate them to full sun otherwise they will burn, like your small one did. I'm not sure why the one that was in the greenhouse did that unless the greenhouse had filtered sun.

Being in a greenhouse all the time can really "baby" the plant. Coming out in the real world can be a shock. Have you fertilized them at all? You can start fertilizing a lotus when it begins to put out aerial leaves.
Its important to fertilize your bigger one. I would use 2-3 pond tabs every month.
I wonder how long its been at the nursery? If its a med-large lotus, it will need to be thinned every 1-2 years.

Well the small one was in a really shady spot last year. This year I moved it to full sun before it even started to put out leaves. Im starting to wonder if its getting too much sun, or the water is getting too hot. My other water plants in pots surprised me over the past couple years, if you stick you hand in the water it is really warm and sometimes hot, but they always looked healthy. Just want to make sure its only acclimating.