HELP: Sudden film in established tank

[basilstorm]

My tank somehow, within the span twelve hours, developed a sort of gray film over the top of it. The rest of the water is clear but the top is gross and it looks like there’s some sort of chunks floating at the top! I don’t know what’s going on, my tank has been cycled since February, the temperature is stable at 68*, I check for my axie’s poop three times a day and remove it immediately. It’s only been five days since a water change, which went completely normal. My axie doesn’t seem stressed but I’m starting to freak out as most solutions only seem to be for new tanks! Could there be something wrong with the filter? It’s been operating as normal but the new water coming out doesn’t seem to be affecting the film and I feel like it should be clean. I’m going to do a full water change tomorrow but I don’t know what the cause it

 

[basilstorm]

Okay so I remember that there was a spider trying to lay eggs on the glass top yesterday and I thought I got everything including the web out but I’m not sure (don’t know if that could even be the cause) so I’m doing a 50% water change even though it’s 2:30 am if this resolves the issue I’ll remove this thread

 

[Murk]

This looks like a fairly regular biofilm: a build-up of proteins and fats and/or the bacteria eating it.

It's not really harmful, though it is curious that it appeared so suddenly, and might be an indicator of something else off-balance in the tank.
The biofilm itself is not dangerous. At worst, it might lead to slightly lower oxygen levels in the tank, but that won't bother an axolotl too much.
If it suddenly appeared because your water parameters are off, that is something you want to solve, though. Do you have any recent measurements (ammonia, nitrites, nitrates)?

There are a lot of "solutions" to biofilm on the internet, but I don't think any of them is really guaranteed to work. Removing the film works, of course, but is a short term solution. I personally have good experiences with live plants (live plants solve basically every problem in an aquarium ).

I also suspect biofilm in cycled tanks can indicate a lack of other surfaces for bacteria to live on, but this is purely from anecdotal evidence. You don't seem to have any substrate - maybe adding some more rough surfaces (or plants!) to the tank would help as well.


In general, though, not something to worry about, though I understand it does look gross. If you can confirm your ammonia/nitrites/nitrates are still good, the tank should be fine.

 

[basilstorm]

Thanks for the advice! I’m thinking of adding moss balls, since a local pet store just got some in. When I did a water change most of the film went away, and my water parameters were all somehow still normal. I have no clue how it happened so suddenly, usually I see a small amount by seven days after my last water change but never this much and never all at once. I’m thinking of changing the pad in my filter, I’m not sure if that would help but it’s probably time anyways