Snail spawn and a skimmer

[asylumdown]

How much snail spooge does it take to make a skimmer go crazy? My total system volume is about 375/350 gallons, and I don't have very many large snails, but twice in the past 10 days I've checked the skimmer right before bed, each time seeing that I should have up to 5 more days of room in the cup at normal production levels, only to come downstairs the following morning to an overflowing skimmer spewing salty water all over the inside of my cabinet.

I can't figure it out, but just a few moments ago I observed one of my larger Astrea snails ejecting puffs of white gunk in to the water. I think I've got maybe 6 of those guys in the tank, not sure if he's the only one doing it. Would that be enough to make the skimmer go nuts or should I be looking for something else still? It's not enough to make the water go visibly cloudy.

The skimmer is a Deltec SC2560, so it's not a small piece of equipment, and it has a relatively large collection cup, it usually takes a lot to make it misbehave.