Have you checked to make sure you're following all the directions on your liquid nitrate tests?
I am, including the laborious amount of bottle and test tube shaking haha. I bought strips because I found zero nitrate to be odd after weeks of fish eating and crapping in my tank.
...a tank that has never shown nitrates may be an un-cycled tank and the fish exposed to trace ammonia or nitrites.
To be clear, it did show plenty of nitrate towards the end of my initial cycle before I put my tetras in. Once that nitrate crept down to near-zero is when I put my fish in.
What is the temperature? Is there any fighting between fish/fin-nipping. Bloodfin tetras have been known to do this.
Nutrition: What are you feeding? How much?
Parasite or pathogen? Are all the fish eating? Any deaths in tank in last month? Any rubbing on objects indicating external parasites? Any white feces?
The fin nipping could be possible actually. I haven't seen that behavior but I have seen them "giving chase" sometimes. When I first put them in there were a couple who would spiral around each other in what looked like aggressive behavior. Now they mostly just school but I do see them chase each other occasionally. I'll try to watch a bit more and see if I've missed anything.
As for food, I've been alternating between Fluval spirulina / algae flake and freeze dried brine shrimp for daily food, and frozen bloodworm once a week. All five of them hide when they hear me at the tank, but after feeding they come out in a minute and eat very enthusiastically. Nothing has died in the tank and I haven't seen any rubbing. Their scales look okay as far as I can tell (they're pretty fast moving so I can't always get the best close up look).
It's completely possible, in fact likely that if you have a tank full of plants and few fish that no3 will register as nil. The plants are consuming any and getting what they need from the soil. Now if you have a heavy fish load and less plants, completely different story.
Thanks, this is what I've been thinking but it's hard to know - there are many different opinions on this...
Basically it’s because it’s smallest filter you can get by with on a 10gal. It only moves 16gph which is just enough to move water and gases around tank but still keep that Walstad quiet water tank feel.
You should also read up on osmotic shock and think about if you may be doing that to your fish on water changes.
Anyway the mignon 60 or 150 (32gph) are only about $17 on Amazon, not bank breaking cost.
Just wanna say that a $16 filter probably cost less than your group of tetras. You don't need anything fancy. You could even do an airstone, you can get a nano usb pump and airstone for $10 from Aquarium Co-op.
In a natural ecosystem, wind will cause natural mixing of the water column. I would suggest at the very minimum an airstone in the tank to promote mixing. There might be ammonia rich pockets close to the bottom of the tank, and your sample from the top of the water column is not reflecting the true amount of ammonia/nitrates in the tank.
The "fishy smell" is usually due to ammonia, by the way. It's gotta be hiding in there somewhere.
It's very easy to have ammonia in a very closed system like a Walstad tank. It runs on a very thin bandwidth of heavy plant mass and light livestock. The whole system is based on loading up on organics as opposed to getting rid of them. Not everything is detected by the inaccurate test kits we use.
All of these are good points. Especially the idea that maybe I'm not getting accurate readings from top water because I have pockets of ammonia or nitrate lower in the tank. You all have almost convinced me to get a small filter or pump. I really appreciate the input!