What is this stuff

[Mundle]

It's on top of the water level

 

[librarygirl]

Hard to tell from the pic. Is it white? Do you have enough surface agitation from the filter or/and air stone? Stagnant water can cause some issues. What's your water change schdule? Water parameters (ammonia, nitrite, nitrate)?

 

[Mundle]

I have a regular filter and two air stones
Change water every week aprox 25-30%
Every so often I go to fish shop to get tested