Possible Precipitation in Skimmate?

Trenton Henderson · Jul 31, 2023

Hi all,

I have posted in the past about the issues I’ve had maintain stable levels of calcium and alkalinity when I have a CO2 scrubber running to raise my pH.

I came across an article (the only one that shared my experience with CO2 scrubbers) that someone theorized that the pH is raised so much within the body of the skimmer that the calcium carbonate begins to precipitate within it. Furthermore, the crystals are carried up into the collection cup, dropping the levels.

When I use my CO2 scrubber, I notice the precipitation in the form of sand hardening in my sand bed. My thought is that for my skimmer, the crystals are formed in the body, and are then ejected from it, sending them to the display and settling in the sand.

It was just a theory until I pulled my collection cup out and noticed this light colored contrast with the dark brown skimmate:

This, at least to me, looks like it’s possibly some calcium carbonate precipitation. What’s your opinion? I think this theory isn’t too crazy. Would love to hear a discussion. I am just dealing with 7.9-8.1 pH now because I want stable alkalinity.

taricha · Jul 31, 2023

If you look at table 2 in this article "Down the Drain" by Shimek.....
https://reefkeeping.com/issues/2002-12/rs/feature/index.php
Calcium is 37,000ppm or 37% of "sludge" from the skimmer.
Since calcium carbonate is 40% Ca, this is pretty good evidence that "sludge" in skimmers is mostly CaCO3.

I don't know if that is because the precipitation happens inside the skimmer chamber, like you suggest, or if it's because fine CaCO3 particles in the water column that get generated in the tank are easily removed by skimming.

It's a good question.

Trenton Henderson · Jul 31, 2023

taricha said:
If you look at table 2 in this article "Down the Drain" by Shimek.....
https://reefkeeping.com/issues/2002-12/rs/feature/index.php
Calcium is 37,000ppm or 37% of "sludge" from the skimmer.
Since calcium carbonate is 40% Ca, this is pretty good evidence that "sludge" in skimmers is mostly CaCO3.

I don't know if that is because the precipitation happens inside the skimmer chamber, like you suggest, or if it's because fine CaCO3 particles in the water column that get generated in the tank are easily removed by skimming.

It's a good question.

The reason I suggest it that way is because I don’t have precipitation unless the CO2 scrubber is connected to the skimmer, affecting its internal pH.

taricha · Jul 31, 2023

Trenton Henderson said:
The reason I suggest it that way is because I don’t have precipitation unless the CO2 scrubber is connected to the skimmer, affecting its internal pH.

I think that's a very logical possibility. The loss of CO2 raises pH and increases odds of precipitation. And it's quite possible that the scrubber being located at the skimmer makes the skimmer a good place for this precipitation to possibly occur.