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First Planted (low-tech), Newb Question

4K views 13 replies 8 participants last post by  Promelas 
#1 ·
I know it's recommended not to have surface agitation with a planted tank, but I've also read that plants CONSUME O2 rather than producing it during the dark half of the photosynthesis cycle. I just planted the tank today, so the roots haven't had time to anchor. Would it be wise to run my HOB (throttled down) when the lights are off? I was going to have a powerhead with a sponged suction as the only mechanical filtration, but my little ebay china made powerhead will blow the glosso's out of the gravel, possibly some of the larger plants too. The HOB just has mechanical filter, no carbon or bio media.
Tank: 65g - 36Lx18Hx12D (I think, I know it's 36L)
Fish: 6 yellow barbs, 7 sword tails, 2 fry
Plants: Amazon swords, Glosso's, Giant Hygro, Lobelia, Blyxa
 
#2 ·
First and foremost, the amount of surface agitation or circulation in a planted tank largely depends on the species of plants. Some plants can't handle it, other plants can't live without it. Another determining factor is location of the plants vs the output from the filter where the strongest amount of flow will come.

I have a house full of planted tanks, all run hang on filters except my 29 gallon biocube which runs a sump system in the back & 75 gallon with canister,. You can check out the photos in my aquariums section by clicking on my name. And yes, I do run carbon in some of my filters, others I have only biomedia in them.

And you are correct about plants consuming O2 during dark hours. Again, the amount they consume/use depends on the species of plant, temp of the water, amount of light during the day, how healthy the plants are, what other nutrients they are taking in, and water chemistry.

Have you yet run this tank during dark hours without a filter? If so, what kind of results have you had thus far and how long has that gone on? If you've done it successfully long term, I would say if its not broke, don't try to fix it. If you either haven't done it yet or have seen a decline in conditions in your tank, then I would say there is no reason not to give it a try if you are keeping plants that can handle it, and as long as delicate plants are not caught directly in the water flow from the filter. Some filters have a stronger outflow than others... that should also be taken into account.

Based on the tank info in your signature, you have a 30 gallon breeder tank. (this is calculating dimensions listed.. and so you have the proper info in the future 30 gallon [US, liquid] = 113.562 353 52 liter)

For the plants you are keeping, if you desired to run a hang on filter just for oxygenation purposes, work with something rated for a 10 - 20 gallon tank, not 30 gallons. This will greatly cut the water flow for those plants that are more vulnerable to the outflow pressure, and be sure the filter is in a location so it is not putting water flow directly on the plants. This may take some time and a bit of experimenting, but shouldn't be too difficult to achieve.
 
#4 ·
The plants should produce enough oxygen during the day to account for the fish night and day, and the plants at night.

I haven't seen this as a problem in my 29g tank yet. I have a small internal filter.

You'll also be able to tell before it hurts you fish if they are lacking oxygen.
 
#5 ·
Just out of curiosity I have a question to add to this topic. I've noticed that people discuss the o2 consumption during the night from time to time and was just wondering if this is in reference to the Calvin cycle part of photosynthesis (aka dark cycle)? The name is somewhat misleading since it doesn't only happen at night, just that it doesn't need light for the reaction. I haven't had to study the nitty gritty details of photosynthesis for some years and I don't remember it all so I was just curious what part of the cycle uses the o2, or if it's independent from photosynthesis entirely.
 
#6 ·
Cellular respriration is what plants do at night, it is also what all animals do. It is a "dark" cycle because it does not require sunlight to "crack" glucose down to CO2 and H2O (and ATP for those bio geeks.) The Calvin-Benson cycle , I beleive, is the syntesis of glucose which requires light.
 
#7 · (Edited)
The "dark" cycle and the Calvin cycle are the same thing, and the Calvin cycle does not require light. The "light" cycle generates ATP which is used for the non-light driven reactions.

Quick edit: I understand that cellular respiration happens in plants, as it does with us, but I've just never seen any scientific article or text that states that this only happens at night. Any text I have ever read has said this happens during the day as well as at night. If you would happen to know any sources that says it happens solely at night I'd be more than happy to read it!
 
#9 ·
I'm a little confused as to what you mean when you say photosynthesis is more efficient than respiration since they're basically two different processes entirely. The point of photosynthesis is to create glucose that can later be broken down to generate ATP by cellular respiration. The benefit of photosynthesis is that the ATP necessary to create glucose comes from the electron flow created by "exciting" the electrons using light within the chlorophyll molecules. If plants weren't able to harness light they would be stuck in a cycle of using ATP to make glucose and then using glucose to make ATP without any real net gains in ATP.
 
#13 ·
I'm a little confused as to what you mean when you say photosynthesis is more efficient than respiration since they're basically two different processes entirely. The point of photosynthesis is to create glucose that can later be broken down to generate ATP by cellular respiration. The benefit of photosynthesis is that the ATP necessary to create glucose comes from the electron flow created by "exciting" the electrons using light within the chlorophyll molecules. If plants weren't able to harness light they would be stuck in a cycle of using ATP to make glucose and then using glucose to make ATP without any real net gains in ATP.
Photosynthesis is WAY more efficient. It produces at total of 38 ATP molecules for one round, while ceelular respriation only produces 2.
 
#10 ·
Plants consume miniscule amounts of O2 constantly. 24 hours a day, 7 days a week.

They convert CO2 to O2 in vast amounts, as a product of photosynthesis. I was worried about that for a while, but there's no need to worry- you're overthinking it. :)

They produce WAY more 02 during the day than they consume, so still more than enough for your fishes and bacteria.

As far as surface agitation though, a little won't hurt. I have a HOB filter in my 10G-


I don't think my plants mind. :)

I think it's the amount of aeration to worry about- a HOB filter, or minor water movement is OK, maybe even good for some plants.
However an airstone is a no no.
 
#12 · (Edited)
I went into this topic in Part 3 of the series on low-tech planted aquaria, but it is apropos to this discussion. First, a summary of respiration taken from Peter Hiscock since I can't say it better:
The process of respiration occurs in all complex organisms and takes place in all plant cells. Respiration helps to break down food sources and release energy into the cells. During the process, oxygen is used up and carbon dioxide is released as a by-product. The chemical equation for the process of respiration is the exact reverse of photosynthesis, except that sunlight energy is not involved. Unlike photosynthesis, respiration is a continual process that does not stop at night. Thus, photosynthesis stores food "energy," whereas respiration releases energy.
In any 24-hour period, the plants release much more oxygen through photosynthesis than they use in respiration. Fish and bacteria are also using oxygen continuously, and more oxygen is used by bacteria than fish (assuming the aquarium is balanced); and this refers to the aerobic bacteria living in the substrate that are essential in the conversion of organics into nutrients for assimilation by the plant roots. And while it may be possible for oxygen to become depleted to critical levels during darkness, this is only going to occur in aquaria that are way over-stocked and not balanced or have supplemental CO2 systems. In a balanced low-tech aquarium, this is not going to be an issue. In high-tech planted tanks, it is much more of a concern which is why CO2 systems should be off during darkness.

With respect to water movement, plants require some in order to bring nutrients to the leaves and roots, but too strong a current is detrimental to their assimilation of carbon via CO2. Excessive levels of oxygen are also problematic for plants, as it inhibits their ability to assimilate nutrients. This is why I advocate minimal water movement and surface disturbance in planted aquaria; going with the minimum necessary is less likely to create issues.

Extraneous water movement is detrimental in two ways: CO2 which is extremely important for plant growth is driven out of the water faster, and oxygen is brought into the water at levels beyond what is good for the plants, which have more difficulty assimilating nutrients when the oxygen level increases. But the more significant aspect is the loss of CO2.

Submerged plants have difficulty obtaining enough CO2 in nature and in the aquarium; this fact is believed by many to be the reason for the inherently slow growth and low productivity of aquatic plants over terrestrial. It also explains why floating plants always grow faster than full-submerged plants--the surface plants can use CO2 from the air. Further, freshwater emerged plants have been shown to be four times more productive that submerged plants. The reason is because CO2 diffuses so slowly in water as opposed to air, and this limits the underwater plant's uptake of CO2 because the CO2 molecules don't contact the leaves quick enough to meet the plant's needs. Aquatic plants have to use enzymes to rapidly capture the CO2. When the CO2 levels in the water become depleted, these enzymes sit idle, so to speak, but the plant still has to provide energy to them. This results in a reduction in photosynthetic efficiency and therefore growth of the plant because energy is being wasted. Thus, anything that removes CO2 in however small an amount will likely be detrimental to the plant's growth. And filtration causing fast water movement will contribute to this detrimental state.

Byron.
 
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