Surface Of Water Covered In Bubbles

[jmeeter]

What would cause something like this? I did an immediate 30% water change and that seems to have fixed it (for now).
 
I have a Fluval HOB filter and a DIY CO2 system. I checked the water parameters the other day and everything was within normal range.
 

 

 

[ImmortalRav]

Bubbles usually just means lots of air inside of your water.

 

[Asteria]

It kind of looks like the dust that comes of the sand when newly added to a tank. As mine did this when filling up. Had not washed my sand as it's coral sand.  Hvery you done anything new in the tank?

 

[Munroco]

Do you have a gourami or betta in there? Possibly its a bubble nest?

 

[Bubbelzzz]

I guess that these are way to much bubbles for a gourami. However it could still explain it.
 
It could be air bubbles from the plants which are generated more due to the CO2. If the surface is polluted there could form a small layer or film on the surface. This will "break" when you poke in it with a finger. This could trap the bubbles on the surface and thus will collect the bubbles that are created by the plants over time.
 
(Can anyone please help me how this layer is called in English? I can't find a translation)

 

[ShinySideUp]

I did a quick look around the nerd-net and there seems to be a concensus that the bubbles may be caused by a combination of low water level and a HOB filter causing too much oxygenation.
 
I do tend to agree with Asteria though, the bubbly sludge looks like detritus from new sand/gravel.