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Blackwater Tank - Bubbles On Surface - Maximum Tannin Saturation?

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What’s up everyone?

A little background info on the tank: 20 gallon long. Tank has been up and running for over 3 years. Started as a shrimp only tank. Then, shrimp and snails. Then, shrimp, snails, and dwarf crayfish. After 3 years of inverts only, it was time to try something new. 

In March I decided I wanted to try a blackwater tank. I ordered up some botanicals, removed all the plants, found some wood that fit well in the tank, and have been steady chucking botanicals in there every week. Sometime I boiled things and made a tea, other times I just rinsed Catappa leaves and hucked em in there. All has been well. 

All, I think, is currently still welll. But, I have some bubbles that have developed on the surface. The other day I boiled a bunch of botanicals, after doing maintenance on all my tanks, made a tea, and hucked the botanicals in there. 5 giant Catappa leaves and 4 decent sized seed pods. This isn’t my first time doing this so I thought nothing of it. 

Went to feed last night and noticed bubbles covering ~1/3 of the top of the tank. I assumed it was ammonia. After all, I did throw a bunch of decaying matter in there, on top of water that was already super dark. I grabbed ye trusty ol’ master test kit, and 0 ammonia, 0 nitrite, and ~20ppm nitrates. Doesn’t seem to be an ammonia issue as I originally thought. Ammonia made the most sense, both because of what I put in the tank, and because of the bubbles, but alas, testing showed 0.

I was doing some general Google searching, as one does, and found that other blackwater/botanical enthusiasts have reported the same. Parameters are normal (again, 0 ammonia, 0 nitrite, and 20 nitrates) but bubbles on the surface. Most have chalked it up to “it’s the tannins” and at this point I have to agree, at least at this point. 

The ONLY thing that changed is I mixed 2 brands of Catappa leaves. I used the last 3 from one pack, and then 2 leaves from a new pack/brand. Had I not boiled them I would’ve assumed maybe there was something on the new brand, but boiling them should’ve taken care of that problem, right?

Idk. At this point I’m chalking it up to “maximum tannin saturation” as the reason for the bubbles, but I can’t help but think it could be something to do with the new Catappa leaves. At this point, everything seems the same, except there’s some bubbles on the surface. Fish look healthy, and all inverts look healthy (shrimp, snails, and crayfish) are still loving life. Testing showed nothing to be concerned about. Happy to take test results again and share pics but as of less than 24 hours ago, and the bubbles being the same, testing was exactly as I expected. 

If there’s any experienced blackwater vets out there I’d love to hear your thoughts. Regardless, this will be a learning opportunity for all of us Nerms! Not panicking, just seeing what happens. Nature is incredible.IMG_4343.jpeg.4bab3148d3bf8876022f66ecba0c7c50.jpegIMG_4344.jpeg.e8390ec82cad4c814ebb4fb028f421f8.jpeg


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I’m happy to report that as of tonight I have a 80-90% reduction in bubbles on the surface. Literally didn’t do anything different; just rode it out and observed to gained knowledge. What caused the bubbles? Your guess is as good as mine. 

I was looking through my pictures and found the first one from when I changed the tank. We went from this:IMG_3576.jpeg.99ab38301fde601e56403eaa83544a92.jpeg

March 2023, pre botanicals

To this:IMG_3608.jpeg.12033a81c870b031a1ceb69b99ebdf2e.jpeg

Some botanicals and some tint to the water. Pre Anubius.

To this:IMG_4364.jpeg.4c71142fd11ba6f34b8527d6c4dc14cb.jpeg

End of July 2023, photo taken 10 minutes ago, with all the botanicals. 

I also love that you can see the Pothos growing through these pictures.

You can hardly see the wood anymore and I love it. Enjoy nature daily, and enjoy your tanks, Nerms. 

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