Thank you all! Mama Platy is giving birth. We're well over 30 fry at this time.
I noticed a few free swimming in the tank, so I netted them and put them in a small container. I put the breeding pen into the tank and transferred mama into it. I know that it's too small, so I'll move her out at the end of the night. But this way I've saved most of them, instead of only a small fraction.
Anyone in San Diego need some Wagtailed Platies?