What type of cauluerpa do you have?
It releases nutrients/spores back into the tank when it goes sexual, not sure I would consider it toxic... Is it good- No.
I had my grape go sexual in my 125 reef 3 times and it looked like someone just dumped a carton of milk into my tank... Did it kill, harm anything, No. I just put some fresh carbon in the tank and took out the now limp, white/clear colored grape caulerpa and tossed it.
I was not running my lights 24/7 and it always went sexual about an hour after the lights came on.
I now have taken all the grape out and run cheto and mexicana and have my lights run 24/7 with no issues.
I would get some new type of macroalgae and toss the grape caulerpa.
no issue spreading to the main tank if it goes sexual. Like I said it happened to me 3 times with no problems... Just a bad looking tank for half a day.