Harmful?

[ROSSELLA1]

Okay, so I was looking at my male betta, Serendipity, and I noticed some tiny white strands of what looked like hairs on the aquarium glass. Since I'd just did a partial water change, I thought this was strange, so I started to look closer to see what areas of the aquarium they're in and I noticed that they were moving! They're about as thick as a human hair and almost an inch in length. They're all white and they move like inch worms do (although they're not like any inch worm I've ever seen).

I'm not sure how long they've been there, but I think I'd have noticed if it was longer than a day or so because I do spend some time looking at my fish every day. I did just switch conditioner (to API Betta conditioner), but they're not in Snow Red's (my female) aquarium, so I doubt it's that.

I don't notice any on Serendipity. He does have some white spots on his front fins, but they've been there for ages (I got him over two months ago and they were there then). I've tried treating them with warm, clean, water, with salt water, with bettafix, and with pimafix, but nothing's gotten rid of them (although they do get smaller in warm water, they don't go away). However, he's never had any ill effects from them and this is the first time I've seen these things in the cage so I'm not sure if they'd be related.

It's a twelve gallon aquarium. The water temp's about 82 degrees. I have aquarium decorations (although none new). I have some snails and some glass shrimp in there, but they've all been there for a while (the snails, over a month, the shrimp, several weeks). I have a java fern, but that's been in there for about a month.

So, I have a few questions:
1) What are they?
2) Are they harmful/ what do they do?
3) If they are harmful, how do I get rid of them?

[Olympia]

1. Probably planaria or nematodes, few other things, nematodes are my guess though from the description.
2. No, none of these little critters hurt the fish, some fish will eat them and it's fine. They just, exist. (So deep!) My filters are full of em.
3. They usually go away pretty quick, just feeding off of extra nutrients, could be some old food in the gravel or something. A water change could get rid of them potentially. Could have come in from your tap, that's what I'm guessing at least.
I've never had a long term problem with nematodes, they seem to come and go.

[ROSSELLA1]

OMG thank you! I was so worried!

[Olympia]

Just to be sure here's a super magnified photo of one.

[ROSSELLA1]

I think that's it.

[SpookyTooth]

They sound more like detritus worms to me, planaria are usually thicker in the body and with an arrow shaped head. I've dealt with nematodes, too and they can look a lot like detritus worms if they are small enough.

If they are detritus worms they are again harmless, they are a result of one of a few things:

* A recently finished cycle
* Excess decaying plant matter
* Excess decaying food matter/fish waste
* New plant additions

It is perfectly normal for detritus worms to be present in an aquarium, they usually stay in the substrate though and will usually only climb the sides of the tank when there is a population explosion due to a multitude of factors (usually one of the above). They can be removed through more regular water changes (with inclusive gravel vacuum), manual removal or fish nommage (my fish would eat the ones that cropped up after plants were introduced). In general, even with increasing good husbandry and such it can take a little time for numbers to decrease. There are a couple of good articles about different microfauna that are available, the following may prove helpful.

http://www3.sympatico.ca/drosera1/fish/worms.htm

It might also be worth searching for detritus worms on google as loads of forum topics come up about them that might offer you some wonderful advice