Mousiekm

Hi, within the past couple months I have been really getting into my aquarium. I have a 50 gallon tank with a Western Painted Turtle and three different types of fish....one is some type of catfish, another is some type of shark (I bought both of those at Petco) and I have a goldfish from Walmart. Everything has been going well in the tank for the past couple months(that's how long I've had it) then last week I noticed those small little hairlike white worms...I cleaned the tank but they came back a couple days later. Those were my concern at first but now I have some weird little white things swimming around and these things are about the size of a grain of salt with a small looking tail (almost like a tadpole look)! I don't know what they are but they are only in one corner of the tank, there is a bunch of them and they just keep swimming in that one spot then they will stick to the glass then swim again. I have been trying to look all over the internet to find out what they are but I can't figure it out! Please help!!