Given the scenario you described, I think it's dropping the leaf because you changed the conditions. Not necessarily that the new conditions are bad, just extremely different.

I would keep an eye on it and keep watering it regularly. I know caudata likes to dry out as much as any other Hoya, but western light is harsh and I think you're more likely to under- than over-water in that location. (At least I am.) I've found that Hoyas either love or hate being put in my western window. I haven't tried caudata yet, so I'll be interested to see what you find.

I do understand, though, that caudatas grow so slow that it's hard to see them drop a whole healthy leaf. >_I have 6 caudatas and most I grow in my aquarium but some I grow in with the other Hoyas. I think they grow slightly faster in the aquarium. The caudata (EPC 662) grows like a weed in there!

///start rant

As I have said many times in the past, I would highly recommend this plant. If you like the look of caudata but have been frustrated by its slowwwwga growth habit (and intimidating reputation) get EPC 662. It's like caudata-for-beginners! Its leaves are different from the other caudatas I have, and when I first received it, it was labeled as "aff. caudata." They are thinner and have a cupping shape, but are still very leathery and rough and with abundant lichen coloring. They are also very hairy. The flowers are typical caudata flowers. It's a fascinating plant.

///end rant

Is there any particular reason you want to combine the two? I assume it's because they are slow growing and you want a fuller looking plant? People always talk about how combining plants forces them to compete with each other, so that might be something for you to consider. It might be they don't grow any quicker together. Setting that aside, if it's something you want to do, I say do it now. You've already upset the plant's rhythm by moving it, so you might as well upset it more. You know what I mean? (I'm using the term 'upset' very loosely here. ^_~)

I haven't noticed my caudatas being overly upset by being moved around. In fact, I consider them pretty vigorous. I'm constantly untwining those hairy little vines from things and it doesn't seem to do them any harm. Maybe you just notice these little setbacks more with caudata because you're more worried about it?

Teisa, to reduce the shock when going from an aquarium to a window sill, you can either open the aquarium cover gradually over a couple of weeks (does not work if you also have other plants living there that do not need to come out and cannot take even temporarily reduced humidity), or you can take the plant out of the aquarium, bag it and otherwise create very similar initial conditions (light and temp as well), and start opening the bag and moving the plant gradually.

Regarding combining the 2 caudatas: if they come from different sources and are or may be different caudata kinds, then I would not combine them in order to have a very good reliable ID. If space is an issue, a communal pot like this can help you save some. But the plants are kept separate inside, as you see. Even this may be too close for fast growing vining plants, as they'll grow into each other, but it's still better than combining them in one pot.

Thanks guys! I guess I didn't realize it may have been from moving it out of terrarium. I was really focusing on keeping it well watered. I've since returned it to aquarium! O:)

I was considering putting them together because of both being small and I am just about to die for a large pot of it, lol! I may just hold off and keep it up for debate!

I don't think you had to return it to the aquarium. If you want it out, leave it out. It's already decided to drop that one leaf, and I don't think it would have dropped any more if you'd left it out. Not that I have a problem keeping it in your aquarium. ;)

I think maybe caudata just takes change hard. When I was reorganizing my plants, I noticed that my caudatas had made a lot of progress and are growing no more slowly than the average Hoya. I think when you buy them, they're just one of those that falls on the long side of adjusting to its new environment before it really gets moving. You might have 2 full baskets before you know it.