If you're positive there's no room, you have options. If it were my pool, I would do a vertical install in the area labeled "SWA." You don't need to use the
Circupool kit as you can use four 90's and scrap pipe to make your own, but here's what it looks like:
View attachment 411932
If you're set on removing the chlorinator and installing the flow switch there, you'll need to reuse the socket on the right. Take a look at "
socket savers." You should be able to find posts here and on the interweb demonstrating use. I've never used one. There are other methods that involve heating the inner pipe and using needle nose pliers to remove it from the socket. If you mess up the socket, you'll be stuck significant replumbing work.