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Signs of low oxygen levels at night?

Miss ATV

Member
Hi all,

I have a question regarding potentially low oxygen levels at night. I am a little bit concerned about this because I am planning to add more fish and don't want them to be uncomfortable or suffer from hypoxia during night time.

I have recently (about a month) set up this 70L tank with the plan to house a small community of fish in it, currently it holds only male A.Cacatuoides as I am still planning what fish to add. In terms of plants I wanted all the plants to be easy low light ones so I stuck to Java fern (normal, trident and petite) and some Anubias nana and nana petite. As floating plants I chose Pistia as it seems to be the only floating plant that does well in my waters. There is no plants in the substrate, all the plants are attached to the wood or floating.
I am running one JBL matten filter and one sponge filter, temperature is set at 25 Celsius and Ph stays at 7-7.5. Substrate is a very thin layer (2cm) of quartz sand. I do about 20% water changes weekly and vacuuming the substrate only picking up the debris from the top.

Out of all the plants the Pistia seems to be doing very well and it grows like crazy to the point that every 2-3 days I have to trim it a bit, I would say abut 70% of the water surface is covered by it. Recently I noticed in the morning when I switch the lights on there are quite a few detritus worms that are on the glass and I'm a bit concerned they are coming out from the substrate due to plant respiration lowering the oxygen levels at night? If this is the case is the fish in any danger? He is always active when I switch the light on and not seem to be gasping or breathing heavy but my plan is to add a few at least 3 more fish so I wonder if adding more livestock will lower even more the oxygen in the night?

What would you say it's a healthy % of plants surface cover? there is enough water movement from the bubbles released by the sponge filter and a little bit from the main filter so I thought it's enough, should I take these little worms as a warning sign that the tank is not oxygenated enough?
 

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ButtNekkid

Active Member
Hi,

I´ve had occasionally almost 100% coverage with floaters (Pistia/Salvinia). Never had any problems. My tank is slightly overstocked.
But your results may vary.

I´d like to get @dw1305 ´s take on this issue. He´s the resident plant guru. :cool:

That´s a nice tank btw!
 

dw1305

Well-Known Member
5 Year Member
Hi all,
......I´ve had occasionally almost 100% coverage with floaters (Pistia/Salvinia). Never had any problems. My tank is slightly overstocked.
But your results may vary.

I´d like to get @dw1305 ´s take on this issue. He´s the resident plant guru. :cool:

That´s a nice tank btw!
Yes, nice tank. I think you should be fine, Pistia doesn't tend to form a complete cover on the water surface, the way a "flat" plant like Duckweed (Lemna minor) would.

cheers Darrel
 

Miss ATV

Member
Hi all,Yes, nice tank. I think you should be fine, Pistia doesn't tend to form a complete cover on the water surface, the way a "flat" plant like Duckweed (Lemna minor) would.

cheers Darrel

Thank you very much Darrel, thats relieving to hear. Can plants actually reach a stage where they deplete the oxygen enough to be worrying for livestock during the night? I am only asking as I would love to add some hornwort too but I was holding from doing so as I was concerned for the fish.
 

dw1305

Well-Known Member
5 Year Member
Hi all,
as I would love to add some hornwort too
Definitely add it. Plants take up ammonia, and nitrite as well as nitrate and that is a massive gain in oxygen terms, because microbial nitrification is an oxygen intensive process.
Can plants actually reach a stage where they deplete the oxygen enough to be worrying for livestock during the night?
They can, but only in certain circumstances. You can mitigate for it by having some flow (increasing the gas exchange surface area).

If fish deaths, attributable to low dissolved oxygen, occur in planted tanks, they always happen at night, because of the extra oxygen demand of the plants. What people don't realize is that when you don't have plants it is always night and their fish would already have died long before that time.

Plants are massively net oxygen producers, you can tell this because one molecule of oxygen (O2) is evolved for every molecule of CO2 bound and plants grow, that growth is the net difference between oxygen consumption and production. It is the net oxygen gain from photosynthesis that gives us an oxygen rich atmosphere and aerobic life.

cheers Darrel
 

Miss ATV

Member
Hi all,Definitely add it. Plants take up ammonia, and nitrite as well as nitrate and that is a massive gain in oxygen terms, because microbial nitrification is an oxygen intensive process. They can, but only in certain circumstances. You can mitigate for it by having some flow (increasing the gas exchange surface area).

If fish deaths, attributable to low dissolved oxygen, occur in planted tanks, they always happen at night, because of the extra oxygen demand of the plants. What people don't realize is that when you don't have plants it is always night and their fish would already have died long before that time.

Plants are massively net oxygen producers, you can tell this because one molecule of oxygen (O2) is evolved for every molecule of CO2 bound and plants grow, that growth is the net difference between oxygen consumption and production. It is the net oxygen gain from photosynthesis that gives us an oxygen rich atmosphere and aerobic life.

cheers Darrel

Amazing thank you so much for the detailed explanation, I can happily add the hornwort then.
 
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