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Comment by RajT88 | Hacker News Reader

You have to tinker a bit. I haven't figured out the role that the bacteria play yet, but too low of oxygen means you need more algae/grass to generate more O2 during daylight hours. (And yes, it will crash at night when there's less photosynthesis)

Don't put too many critters in there either. Mine is pretty stable for a few hours now with 3 fish, and ample grass and algae.

Side question: Is it in my head, or are the fish slowly growing?

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For bacteria: I believe their role is to provide nitrogen in the sand by eating algae poop. Nitrogen in the sand is required for plants in that sand to grow.

You can test this a bit:

1. Create a new sphere and fill it with water. Add a bit of sand at the bottom

2. Add algae and fastforward.

3. The algae will multiply, causing the o2 to shoot up.

4. The algae will die off because of the high o2. Their dead bodies (purple dots) will litter the sea floor.

5. Put in some bacteria.

6. You can watch the bacteria eat the purple dots. Note that the sand changes color slightly as they do - I think that's the sand becoming nitrogen-rich.

Yes the sand seems to darken a bit under where bacteria were eating, that might be the nitrogen, although it doesn't seem to spread over the rest of the sand, not sure if the plants are getting it.

Also you need to keep adding bacteria because the keep dying off. They don't have the mobility to find all the dead algae, so they are gone pretty quickly.

You need a nice wood tree in the tank, can increase your grass area a lot

Yeah, they grow.

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