squirming things in my fish tank

Question
what are these squirming fisl-like things in my  40 gal fish tank, when i clean the sides, they seem to appear.my sides develop brown alge. what can i do to clear up. just two weeks ago, i cleaned down to the stones, and today you would never know it.

Answer
Dottie,
I would need a bit more information to really ID these things.
to hazard a guess I would think they are some sort of planeria worms feeding on excess organic material in the system.
I would also guess that you either have a tank with larger fish, or one that is heavily stocked.
Either of these conditions along with what you feed the fish can contribute to this condition.
They are really not dangerous and don;t hurt the fish.
However, you may want to take extra care in making sure the organic material is kept to a minimum.
Vacuuming the gravel is a good start as is changing water on a regular basis, 5gals a week is a good starting point, more frequent changes at the same gallonage if needed.
Brown algae is of course a nuisance algae and a lower light algae than green, when the food source is removed the algae will die off.
You may want to check your lights if the bulbs have not been changed in a while, typically 8-12 months.
If you have additional concerns feel free to ask.