if plants produce oxygen and like co2 why cant u just add more fish?

[Fordtrannyman]

Being a little over-technical, maybe, but:

Plants do not "go into reverse" at night; they are respiring (using O2 and releasing CO2) all the time, just like animals. But a healthy plant, when exposed to light, is a net producer of O2 and a net consumer of CO2. When not exposed to light, photosynthesis stops and only respiration is occurring, so they become net producers of CO2 and net consumers of O2.

That may have been what you meant, but I just thought I would clarify.

This is a good explanation.
Try this experiment; Cut all available light, including ambient light by blanketing the tank for 7 days. Uncover and you would be amazed at the jungle. This proves to me that photosynthesis does not completely stop as long as there is a source of available nutrients in the water column.

Good question Zeta!

 

[KarlTh]

This is a good explanation.
Try this experiment; Cut all available light, including ambient light by blanketing the tank for 7 days. Uncover and you would be amazed at the jungle. This proves to me that photosynthesis does not completely stop as long as there is a source of available nutrients in the water column.

Good question Zeta!

It does; however, there is a reservoir of sugars formed in higher plants which allows them to keep going temporarily in darkness. Once this is exhausted, the plant will stop growing, because without light it cannot process CO2 into sugars.

More specifically, there are two stages to photosynthesis - the light reaction, which can only occur in light because light is needed to start the chemical cascade, and the dark reaction which turns the products of the light reaction into sugars. Again, whilst those products are still available, the plant will continue to create sugar using the light reaction. But once they're used up, that's it, until there's more light available.

Lower plants, like algae, do not have these reserves. This is why 48 hour blackouts kill algae whilst leaving the higher plants alive. A long enough blackout, which will depend on the plants, will eventually kill any plant.

 

[plantbrain]

Try that test for 1 month then since the plants "grow". If your theory is correct, then we should see more dry weight biomass at the end of 1 month in the dark.
The key is new dry weight biomass, extension due to being blocked from light is a normal plant response.

They cannot move really, so they "stretch".
Some aquatic plants will autofragment if exposed to a number of different things like blackouts or nutrient decline etc, it hopes of the fragment landing somewhere better.

Algae, at least most species do have reserves(Chara, Caldophora, GSA, GW, GDA all have ample reserves, and are similar to higher plants(most of these use the same storage product, starch, diatoms have excellent storage products: chrysolaminarin) but rather than focusing on those, they are able to use different life stages, and can produces spores, that wait again for good nutrients, CO2, light etc to start regrowing.

Much like an annual plant that produces seeds to get through the dry harsh winter etc.

Algae are very similar, they produce spores instead.
BGA etc can be controlled via a Blackout, but the spores are still there and can grow back in a few days if the root issue(typically neglected tanks or low NO3) are not addressed. Antibiotics will also kill spores however.

Aquatic plants are much much larger and can draw nutrients from many other areas, roots, stems, older leaves etc.

But aquatic plants need far more Carbon(as well as everything else) than algae do also, algae do not have nearly as much support and structure to build.



Regards,
Tom Barr