Skimmer keeps spontaneously overflowing.
 

I have a csc250 on my 100 gallon total volume system.

I have it set to skim fairly dry (the neck and body get pretty dirty with skim mate). The cup fills fairly slowly.

But lately the skimmer seems to go crazy and overflow for no apparent reason.

Anyone have any idea why this would happen?

Something stuck in or dirty air intake?

I always found that one of the most overlooked skimmer adjustments is how deep in the water in your sump it sits.

Try building a stand for your skimmer out of egg crate (or anything, I always used egg crate because it's handy and easy to clean/adjust) and raising it inside your sump.

Then set your skimmer to skim to your preference with the new depth.

This might not solve whatever is changing in your water column to create more skimmate all of a sudden, but it will stop your skimmer from overflowing when that does happen.

My skimmer is already on a stand and at optimum water level of 8"

Air intake is also clean

Any epoxy used lately? That usually makes it go nuts.

That happened with mine, had salt creep between the pump intake and the air hose, so it would occasionally go berzerk. (I had to disassemble the pump to access the part that was clogged.) I gave it a very thorough cleaning and have had consistent skimming since. Make sure there isn't any salt creep/blockage along the air intakes.

Check the venturi on the pump. If it is starting to build up with salt it could make the skimmer a lot touchier. Might just need a good cleaning all around.

Alright.

Well, if you continue to have your skimmer overflowing issue, please think about raising it a little more and adjusting your skimmer....it can't hurt.

How long have you had the skimmer? When did it start this random overflowing? When's the last time you gave the whole thing a good vinegar bath including the venturi? Fwiw, I also think that considering the water depth is a reasonable step. manufacturer recommendations don't always turn out to be the best. Setting a tile or two under the skimmer might be an easy solution.

Fwiw, skimmer sizing has more to do with display volume than total system volume (within reason). This is because of the potential bioload, and generally the bioload is a direct reflection of the display tank size. Do you have a very light bioload?

When my Skimz SK181 (pretty much same skimmer) did this I found Ca built up in the venturi just below the airline fitting. This was a few months from new.
I now clean the venturi weekly and it hasn't puked in years.