[Delphinus]

In my experience it's a case of "they might or they might not, but they probably won't."

I've always kept my photoperiod constant and I had caulerpa and halimeda sporulate.

Basically there's really no control of sporulation - it either happens or it doesn't. The only thing you can do to mitigate the risk is keep pruning so that if it does sporulate, at least it's (hopefully) only a little bit of it that does.

I've found chaeto can be a frustratingly slow grower. One thing that I've found, it does seem to grow faster under brighter lights so you can consider adding some light (maybe a second CF, or a bigger CF, or something like that). Also I've noticed that it sometimes just sort of sits there and does nothing, but when it starts to grow boy does it suddenly take off on you. So it could be a case of that down the road it will be growing quickly for you.

There have been times I've been tempted to see if I could get some caulerpas again but I'm really not sure if there's a way to guarantee it doesn't spread into your main display. There are some neat caulerpa species though. I'd love to get my hands on some C. prolifera for example, looks almost like seagrass. I haven't seen any locally though... if you find some please let me know!