Ok so about a month ago I took my 47g apart completely and cleaned and started it all over again. Everything is new, water and filters media. It's been running now for about a month waiting to cycle. So here's the weird part. I was walking past it yesterday, did a double take and took a closer look. At first what I thought I saw at a glance as fish poo I quickly realise it can't be that there are no fish in it. I back tracked and took a closer look and realised I was looking at the bottom of the tank crawling with red worms. WHAT! how can that be? I thought. I still don't know. Well knowing my Bettas love them I put about 10 females in there and with in about two minutes they were history. I pulled one of the filter medias up to look at it and they are in it. So does anyone have any idea where they came from?

What substrate did you put in? Anything at all reused between the tanks?

Kind of sound like blood worms larva but I don't know where they might of come from haha.

typicaly blood worms or black worms require a cooler temp and faster moving water to stay alive. but if you have fed live blood worms im shure some survived.

No I wasn't feeding bloodworms. There were no fish in it at the time. It's a bare bottom tank. The only thing I put in it was a little water from the apple snail tank to help cycle it but there are no bloodworms in there tank. Everything in the tank was new. I had emptied it out and cleaned it dry before refilling it.

Do blood worms do survive, do they do anything helpful or harmful? I'm sure they're fine, just that Worms are associated with bad usually

Although not normally so red it could also be mosquito larva. Just a guess though.

Your red worms are larve for a midge fly. We have midge flyr here. Also you could get them from flake food. Just a normal event

Sorry for the typo.

it sounds like just a free source of food to me

There was no food of any kind in the tank. There weren't any fish in it.