Hi! It's me again! I've had to polish two of my older canas. They chose pink
This is how I held her to paint her shell:
This is a younger cana with a fairly healthy shell:
What I'd do with your snails is to dry them off gently with a towel--very gently. If there is algae on the part you want to paint, you can remove most of it with a very soft toothbrush--or just dry it well and leave it. Their shells may be delicate so don't scrub them too hard!
Then hold them like in the picture and start painting them. I held mine in this position for about 15-20 minutes and then put her in a shallow plate of tank water till she dried thoroughly and then put a second coat on. I let that dry thoroughly and then put her back in the tank. If you think your snails need a third coat, I'd wait and do it later in the day or the next day just to be sure the first two coats are completely dry.
This will keep their shells from eroding any further. You can use any color or any brand of polish. I used Sally Hansen Diamond Strength because that's what I used on my own nails. The polish has been on her shell for over 3 months now. You'll know when it needs to be touched up.