What is in the skimmate produced by a protein skimmer?

What is in the skimmate produced by a protein skimmer?

what is in protein skimmer skimmate

It certainly isn’t sugar and spice and everything nice. The ooey-gooey smelly gunk inside the collection cup of my protein skimmer is a nasty, brown sludge. From a visual standpoint, there isn’t a single characteristic of that mess that seems like it belongs in my tank. But I got to wondering…what is in the skimmate produced by a protein skimmer?

Luckily, Google knew what I was looking for.

The answer

protein skimmer collection cup

According to Ken Feldman, author of that article and study, skimmate is made of:

  • 38% organic carbon
  • 26% calcium carbonate
  • 21% silicon dioxide
  • 8% inorganic ions (trace nutrients?)
  • 7% magnesium carbonate

I was a bit surprised by these results, because the whole ‘point’ of a protein skimmer, or at least I thought, was to remove dissolved organic particles. But even though the skimmer did remove a sizeable amount of organics from the tank (38% in the case reported above), the authors of that study noted that the majority of the organics removed was insoluble carbon, not the dissolved stuff they thought they would remove.


Another surprising thing (sort of) was the amount of calcium carbonate removed. Clearly, our tanks have a lot of calcium carbonate in the water—that’s not what is surprising, but most of us spend a lot of time trying to ensure calcium levels stay high in our tanks, but the results of that study suggest that our skimmers may be sucking the calcium very literally out of our tanks.


So what are we supposed to make out of all of these data (which are not new, by the way, they were posted in 2010—they are just new to me)?

For one thing, it does reinforce my belief that the single most important thing to do, as a hobbyist, is the inglorious, yeoman’s work of the partial water change. It also makes me wonder if I need a protein skimmer at all. Still, it’s hard to look at that nasty collection cup and think that stuff belongs in my tank.

skimmate collecting on lid

What do you think? Are you surprised by any of this? I guess, kind of like hot dogs, I was a lot happier about my skimmer before I knew what was in it.

Maybe I’ll go eat a hot dog now. But before you go. You can download my eBook FREE.


super tiny download buttonClick here to download a free eBook: Avoid the 5 MOST COMMON Saltwater Aquarium Mistakes








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