Anyone know what this is?

[Al]

This appeared in my tank over the period of about an hour, and i'm really not sure what it is...

My water seems to be normal, pH-6.8, 30deg C, NO3 < 5mg/L, NH3 < 0.01.

I've just added CO2 injection to the tank, with a controller, but at an extremely slow rate < 1 bubble per 5 seconds.

I did a water change earlier today, everything was fine.

The discus seem to be pecking at it, but don't seem to like the taste, and are generally leaving it alone. The only other fish in the tank are 2 Siamese algae eaters, two bristle noses and 12 cardinal tetra's.

I'm not terribly worried about it, should I be?!

[Chris McMahon]

Would you be using a DIY yeast injection system by any chance?

[Al]

No, pressurised CO2...

I removed it, it was like some sort of mucus.

[Chris McMahon]

No, pressurised CO2...

Hmm, usually that white stuff is yeast that escapes people's DIY yeast-based CO2 generators. I haven't heard of it with pressurised tanks though.

I usually recommend a gas separator as described here. It might be worth a try if the problem persists.