After talking about it for a long time, we finally implemented the fish tube: a fish-sized tube connecting our two 10-gallon aquaria.
February: We add gravel and plants to set up our
second tank.
March-April: Many
water tests on the new tank to ensure it's stabilized. One treatment of erythromycin in response to a blue-green algae bloom.
April-May: More water tests.
| Date | Tank | NH4 | NO3 | PO4 | pH | GH | KH | Notes |
|---|
| 4/30 | Old | 0 | 5 | 0.5 | 7.6 | 5 | | |
| New | 0 | 5 | 0.5 | 7.6 | 4 | | 20% water change, started erythromycin |
| Tap water | | | | 7.6 | 3 | | |
| 5/1 | New | | | | | | | Nitrogen fertilizer, erythromycin |
| 5/2 | New | | | | | | | 20% water change, erythromycin |
| 5/3 | New | | | | | | | erythromycin |
| 5/4 | New | 0 | 10 | 2 | 7.2 | 5 | 4 | 20% water change, added nitrogen |
| 5/7 | New | 0 | 5 | 1 | 7.6 | | | 20% water change, added nitrogen |
| 5/11 | Old | 0 | 5 | 0.25 | 7.6 | 4 | | |
| New | 0.25 | 5 | 0.5 | 7.6 | 5 | | |
| 5/19 | | | | | | | | Fish tube, 25% water change |
| 5/22 | New | 0 | 5 | 0.25 | 7.6 | 5 | 4 | Two tanks hopefully equilibrated |
The Fish Tube
The fish tube is a clear rectangular tube, 1.75" x 2.25" in cross section (inside dimensions), constructed of acrylic held together with Loctite 3321 UV adhesive. It is shaped like an inverted U with a total length of 15" (measured along the center line).
It bridges the two tanks and provides a path through which our fish can swim from one to the other. Unfortunately, this is the furthest into the tube that the fish have ventured so far:
I also hoped the tube would allow stuff to diffuse between the two tanks. I tried to verify this using some quick calculations:
Using a
published diffusion rate of 1.8×10
-9 m
2/s for ammonium at 25°C and approximating the fish tube as 0.38 m long, Fick's law gives us
J = -(4.7×10
-9 m/s)Δ
φ, where
J is the diffusion flux (mol/m
2s, say) and Δ
φ is the concentration difference (mol/m
3). The tube has a 2.5 × 10
-3 m
2 cross-sectional area and each tank holds 40 L, which gives us d
φ/dt = (0.063 m
-1)
J for each tank, ultimately yielding:
dΔφ/dt = -(5.9×10-10 s-1)Δφ
which has a time constant of 54 years. Looks like molecular diffusion is not a significant factor. So we have to rely on macroscopic mixing due to flow within the tube, which I'm not able to characterize so easily. But I think it's probably happening!
Update (May 24): One rasbora in the new tank! He must have...gotten lost or something. But perhaps they'll start getting used to inter-aquarium travel!
Update (May 26): We decided the rasbora in the new tank looked pretty miserable being by himself, and probably wasn't there of his own volition. We chased him into the mouth of the tube using a net, but he was very reluctant to go further up the tube (i.e., above the water line). We started pushing the net into the tube, which finally encouraged him to get over his fears and enter the tube. He looked very confused, then swam quickly across the tube and back down into the old tank.
Update (June 5): Getting ready for our China trip. Stuffed some stem plants into the tube to prevent the fish from getting lost again. To keep the water chemistry more stable, I added a drain tube to siphon water from the new tank's filter into the old tank, creating circulation. A little worried because blue-green algae continues to be a problem in the new tank, but I am hoping that joining the two will provide the proper balance of nutrients to encourage plant rather than algae growth. Of course, it could go the other way, and we could come home to find both tanks overrun with cyanobacteria...
Update (July 23): Cyanobacteria still abounds in the new tank, though the old tank seems unaffected. I put snail into the new tank to eat the brown algae. He cleans it off very effectively, but he random-walks around the tank, so there are many areas left uncleaned.
The night before last, we found a rasbora sleeping in the fish tube! He was the slightly off-kilter one. We didn't know if figured out how the fish tube works or if he was just lost. In the morning, he was back in the old tank.
Last night, he was back in the tube! And later that night, he was sleeping in the new tank. This morning, though, he was pretty freaked out and trying to swim back to the old tank by running into the glass. I fed him, but he was too freaked out to eat. I chased him into the tube and had to push the net into the tube to get him to go above the water line. He's back in the old tank now.
Update (July 26): Yesterday the Oto made his way through the fish tube! He spent most of the day swimming frantically in the new tank. That night, he found his way back. At the same time, a rasbora (probably the same rasbora as before) spent the night in the tube and was in the new tank in the morning. He's still there.
