Like i said the very first post here. The shop is also at fault here, they should of explained about cycling and not sold incomparable fish.
You should quiz them when they test your water and see what response they give.
If you don't get a good answer then i would find my self a better place to get fish.
Also the only reason i though u had not cycled the tank also in the very first post is coz of your title here.
"An hour after buying a tank, I have babies" this dose not sound like u left the tank for a week.
Also getting to the pleco's now.
Pleco's have been known to actively hunt fry.
I had a bristlenose that used to sit in the front corner of the tank all day. I had noticed fry was going but was never sure and did not think of the pleco at the time, then as i was watching them one day a fry swam over in to the corner, next of the pleco and it pounced onto it!!!
It's not a case if they have enough food or not, it more a case if they lurn to hunt. Fry must taste better than algae!