Something strange in the tank

[petaRJ]

So i've had my tank set up for about 2 weeks now and my axy has been living it in since Friday. Something is stuck on the sides of the tank. I'm not sure if it is from where I fed him brine shrimp and then put him back into his tank with it still on me and him. But i've never seen it before. I fed my big kids (55 gal tank) the brine shrimp and I don't see it on that tank. But however that doesn't mean anything because the fish in that tank eat it up pretty quick. Oh and one other thing since I have a small filter should I still do a 20% water change once a week?

 

[sde]

If I am looking at the right thing than it just looks like residue?
You should do a 10-20% water change every 1-2 weeks regardless of filter size, if the tank is cycled and established.