Well, I gave it the old college try. For two months I ran my 187 gallon reef tank without a skimmer. Why did I do this? The primary reason was a nine month battle I was having with cyanobacteria.


Cyano prefers higher C02 and my skimmer sits in a sump in the same room as my furnace, a potential source of C02. In theory, shutting down the skimmer should have lowered C02 in the tank since the skimmer’s air intake is supposed to equalize C02 levels between the air and tank water.


After receding a bit at first, the cyano eventually became even worse, covering most of the sand and a good percentage of the live rock. My nitrates didn’t go up but my phosphates had climbed.




Going Skimmerless – Impact on pH

What about my pH? It did rise slightly to 8.3 during the peak of my light cycle, an indication the tank was receiving less C02 without aeration from the skimmer. One other thing to note, before I turned off the skimmer I did run some tubing from my skimmer’s air intake through a utility window in the basement to try and bring in less C02 rich air. Unfortunately, I did not observe a rise in pH or less cyano.

After I turned the skimmer back on my cyano did not retreat despite trying other things such as performing larger water changes and feeding the tank less. Interestingly, the chaeto in my ARID algae reactor was not growing as well while my tank was skimmerless, a key reason, I believe, the experiment failed since nutrient export was weak. In fact, it was not growing great while the cyano was in full bloom before and after the experiment.

Chaeto Growth Takes Off Without Cyano

About five weeks ago I did eradicate the cyano and since then my chaeto has been growing like gang busters. Why did the chaeto take off? I believe the cyano restricted chaeto growth since the cyano acted as the dominant form of nutrient export.




Now that the chaeto is growing, would my tank do well without a skimmer? I think it would but things are going pretty well so I am going to pass, for the time being, on trying that again 🙂


Interested in learning more about how I won the battle with cyano? Stay tuned….I will have an update very soon.



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If you are looking for additional insights and information, please explore my many other reef tank and SPS related articles as well as my book, A ReefBum’s Guide To Keeping an SPS Reef Tank: A Blueprint For Success. Additionally, you can see all of my reef tank videos online now as well as my Live HD Webcam.


Happy reef keeping!