Oh ok.
Well there's no way they could really have populated enough bacteria yet in 3 days to affect anything (either positively or negatively), and since they are basically plastic otherwise, they're basically inert in and of themselves, so very likely that is only coincidence.
To me the fact that spring equinox was only 5 days ago is the more striking coincidence. I found that with my anemones very much so and yeah that could also be coincidence but the fact that it happens more often than not is probably telling us there is something to that after all.
Wish I was closer, I'd come over to help. Just make up as much SW as you can for tomorrow (or anytime after you notice them stop spewing, really) and kick off that waterchange. Do another one in another day or two if need be. Waterchanges can't really hurt and "the solution for pollution is dilution" so they definitely help in that way.
Another though. Sorta hesitant to suggest this since you had a bad experience with it, but when I had my mystery cloudiness back in September, I first thought it was a spawn. But then I noticed it wasn't clearing as quickly as other spawns I've had. It was suggested to me to use Coral Snow (the zeovit stuff) to help clear the water and I think it did help clear the water in the end.
But that was really a strange one for me and I'm not sure it was a spawn in the end since the water usually cleared up in a half day or so for those other spawns.
Good luck!