Bio film build up? could be in the hoses.

How much surface agitation do you have? I had a section of my sump where I had nearly no surface movement what so ever. The water flowed so smoothly over the baffles that there was no surface movement and I found I had a slight film develop over it in time. I just assumed it was an accumulation of something, either protein the skimmer didn't get a chance to remove or a byproduct of one of the tanks inhabitants.
All I did was move a piece of equipment that roughed up the flow before a baffle creating some wave action across that section and I've never had it again.

+1 my foxface does that too

From Reef Central
"The fish is definitely shedding its cuticle...nothing to worry about. it's not really a mucous layer, but more akin to a reptile's skin, altho not "quite". Lionfish and other Scorpioniformes do this on a regular basis, and it's one of the reasons these fish are disease-resistant.

Here's a vid showing our volitans molting:

LIONFISH SHEDDING CUTICLE "

cont...
I had my local genius at the fish store tell me it was the mucous layer shedding. He said that venomous fish do this to restore their defenses."


Hope that helps,

Yep it's the foxface, when the fish gets to be 9" long, the sheets of it are huge and get tangled up in the corals

Huh ... there's my Friday 'you learn something new everyday' intake

OK then, you've convinced me and I'll start watching the fox more closely

Thanks for the help everyone

Sorry I doubted you Madreefer :wink:

Update ...

Thanks again everyone for your input
Since the Fox sold I haven't seen any more slime
I haven't been watching the tank as much lately, but so far so good :smile: