Hello, Thanks, and a question...

First, new to the hobby, and this forum, so HI!

Second, Thanks to the great advice I have read on this forum, I have successfully populated a 7 gal with 2 neon blue gouramis, and 5 rasboras. As well as a 10 gal with 8 neon tetras and 4 zebra danios. All are happy and healthy, as far as I can tell.

Now the question...

Does anyone know about how often danios or tetras spawn?

I'll explain in a bit.

So I'm doin' a water change and gravel vaccuum on the 10 gal, and as I'm gettin' ready to pitch the old water, I notice what appear to be frye in the bottom of the bucket! I let the water settle, and sure enough, that's the case. So I've already replaced the water in the 10 gal, and I'm freakin' out tryin' to replace the frye in the tank, and it's not workin' out, and to make a long story short, (too late ), the baby got thrown out with the bathwater, as it were.

I don't want this to happen again, so my concerns are...
how often might this happen? How will I know it if it does? Will I be able to keep from vaccuumin' them up again, or what?
and if I do suck the poor little souls up again, is there some ingenious way to replace them, and not the old water?

Thanks in advance...