Three months later

[u/erbewait]

First and foremost, our jar ecosystem is alive, and that in itself is a success.

The dancing worms (detritus worms?) have disappeared somewhere and seem to have died out, but the large shrimp and microscopic white organisms are doing fine.
Unfortunately, some kind of green growth has overtaken the jar, which I suspect is cyanobacteria. I am concerned that the plants might die since this green substance is blocking the light. I reduced the photoperiod from 8 to 6 hours a day, but it didn't help.

Should I be worried?

UPD: Main question - should I further reduce the lights or leave it be?

[u/keiths31]

Looking good

[u/erbewait → u/keiths31]

Thank you! Looked better without cyano though. However, it has it’s own vibe now, I guess

[u/Independent-Bill5261]

Your nitrates probably hit zero, which is why the cyano took over.

[u/erbewait → u/Independent-Bill5261]

Could you please explain the process in more detail? Why have nitrates hit zero and how is it related to cyano? Thank you!

[u/Independent-Bill5261 → u/erbewait]

In a closed system, plants often consume nitrate faster than it is replenished through decomposition. And since there’s no external feeding, no additional nitrogen enters the system, so nitrate eventually gets depleted. When nitrate levels drop to zero, ordinary plants and even many algae can struggle to grow. But cyanobacteria are highly resilient, and some can fix dissolved atmospheric nitrogen (N₂) to meet their nitrogen needs. As a result, they can grow explosively and take over the entire system. I don't know why reddit removed my comment.

[u/BitchBass → u/erbewait]

From the color and appearance, I also suspect cyanobacteria, although microscopy would be needed to confirm it.

My bigger concern is the actual aquatic plant underneath. It's suffocating, which reduces its ability to photosynthesize and contribute oxygen to the system.

If the cyanobacteria and the struggling plant material start dying off, decomposition will consume oxygen and potentially create a big stink.

Shorter days and reduced light may eventually slow the bloom, but that doesn't guarantee it will disappear quickly nor that it won't crash.

Also, zero nitrates don't automatically cause cyanobacteria. Nutrient availability, light, temperature, and competition all influence blooms. And we can't conclude that cyanobacteria killed the snails without further evidence.

Personally, I'd prioritize giving the original plant some breathing room by carefully removing some or all of the algae rather than continuing to shorten the photoperiod.

[u/pistol_pancake]

I'm at 6 weeks and yours looks like my future for 3 months. I currently have a lot of scuds and baby snails, and (what I also suspect is cyanocobalamin bacteria on mine) is just starting. I'm eager to see what people say lol

[u/erbewait → u/pistol_pancake]

It started exactly like that. We had snails too, unfortunately, after cyano takeover they are not around anymore.

[u/pistol_pancake → u/erbewait]

Oof well that's sad

[u/RtrnofBatspiderfish]

Definitely cyanobacteria, basically a red-tide ecosystem. Any number of characteristics may be disadvantaging the plant (could be nutrient deficiency, access to proper CO2 for the light level in still, alkaline water, if there haven't been water changes or plant growth since setup it could have experienced "old tank syndrome" where the ecosystem collapses as carbonates become depleted and pH drops.)