Nano issues: substrate bubbles, duckweed
I have a natural / "Walstad" style five gallon hex at work, my first planted tank, and it's doing great! There are two minor, quibbling issues I was hoping to get advice on.
First of all: the substrate is about 1" soil with a 1/2" sand cap. The soil is probably too deep for such a small tank, but there isn't much I can do about it now. There are air bubbles in the soil. Occasionally (when a drawer is closed, or the chair bumps the desk, etc) they're released. They don't seem to be "anaerobic bubbles of death!" yet and don't seem to be doing any harm, but should I be concerned? Is there anything I can do about them, aside from poking at the soil with stick?
Secondly: added duckweed and giant duckweed about a week ago. And they have been steadily dying since.
Based on what little I know about duckweed, I'm thinking there's not enough nutrients (ie: decaying stuff) in the water to support them. This leads to a few other concerns.
A) I added the duckweed in hopes it would cover the surface and help slow the evaporation some. I'm going to cut some plastic to cover the top, but only about 1/2 of it due to emergent plants. Any other suggestions?
B) All the other plants right now have roots. So they can get to that nutrient-rich (air-bubble-filled) soil, no problems. But this does not bode well for any other floating plants I'd like to add. In the long term, I'm wondering if there isn't enough livestock to support the plants (without ferts), but the tank is so small, it's too easy to overstock.
At first I thought the dead duckweed would start to rot and, in turn, feed the surviving duckweed but that doesn't seem to be happening. Also the dead duckweed looks pretty awful.