If so, do you know if it'd possible to split the volumes on the keyboard? I'm finding the volume on the lower part of the keyboard is too loud, and I'd like to reduce it. The manual only talks about splitting tones, not volume.
Any help appreciated.

I don't have the WK-1800 (although I still have a very old WK-1200, used to have a WK-3000, and a WK-3500, and currently have a WK-3700 and a WK-7600.

I don't think you can control the volume for the split separately. You might be able to go into the patch editor and adjust volume output there (I'm just speculating), but that sets for the instrument itself and will apply when you use it as a solo instrument as well. I don't remember if the WK-1800 had user control software (my 3500 and 3700 do, but I don't know when they introduced that).

The only real volume control (other than the main volume control) is to adjust the accompaniment volume relative to the melody instrument volume (I used to have to mark my music with the appropriate settings so the accompaniment wouldn't drown out the melody).

Hi John,
Thank you for your response - I think you're right, it can't be done. I'll just have try and back off my left hand a bit.
Wow, you've had quite a few Casios - you must like them. I love mine, but I bought it my accident. About 20 years ago I decided to start playing again after a 10 year hiatus. During my band days I always used either Yamaha or Roland and that's what I intended to buy.

In the music store they had a lot of different keyboards lined up so I just started at the beginning and had a play on all of them. When I found the one I liked I decided to buy it. As I was paying I asked the salesperson, "By the way, what brand is it?" and he replied "It's a Casio" I was shocked; I'd always thought of Casio as a kids toy that your buy in a department store that has lit up keys and cheesy accompaniments.

My how they'd changed.

Incidentally, as we were completing the transaction I asked if he knew of any software that I could use to do arrangements. He reached behind him and said "You need this. it's called Band in a Box"

And so began a long lasting relationship .......