substrate becoming anaerobic

[Evan Baker]

How do you keep the substrate in a planted tank from becoming anaerobic?  Or what causes the substrate to become anaerobic?

 

[AnimalNerd98]

As I understand it, a substrate becomes anaerobic when there is little to no oxygen present in the substrate. This allows for the colonization of anaerobic bacteria who can convert nitrate into nitrogen gas (denitrifying process). There is a whole side of the hobby dedicated to utilizing anaerobic bacteria for biological filtration. This can be accomplished by having deep substrate beds (several inches thick) and/or using substrate that can compact very well (very small grains of sand). 

To prevent most of the substrate from becoming anaerobic (anaerobic pockets can possibly form), you can use larger grains for the substrate like gravel or Eco complete. You can also keep relatively shallow layers of substrate (only a couple inches thick). You can also introduce fish or inverts that churn the substrate. Kuhli loaches and Malaysian trumpet snails will burrow in substrate while Geophagus will take gulps of substrate and filter it out of their gill plates. You can also just churn it up yourself by gravel vacuuming, but if you have a planted tank, you don’t want to disturb the substrate too much. 

[nabokovfan87]

On 8/12/2022 at 5:36 PM, Evan Baker said:

How do you keep the substrate in a planted tank from becoming anaerobic?  Or what causes the substrate to become anaerobic?

It depends on what you're doing.  anaerobic bacteria isn't a negative thing. The issue is the pockets of hydrogen sulfide gas that could be deadly. 

If you're using sand, or a fine substrate, when you gravel vac you'd just want to disturb the substrate.  Some people use chop sticks to do this as well or the handle of a net, aquascaping spatula, etc.

If you're using gravel, I don't think it's too much of a concern, but you'd just make sure flow doesn't have the major dead spots, then you'd want to gravel vac it and make sure you're not leaving a massive amount of waste trapped in those dead spots. 

If you're using a soil or planted substrate, typically you wouldn't gravel vac as well, but you do want to make sure things aren't just heaping piles of waste and nitrates everywhere.  Stirring things up and using a turkey baster is a common method I've seen that I would recommend.  Again, you can use a net, spatula, something to get things into the water column and then siphon that excess off.
 

 

[Patrick_G]

On 8/12/2022 at 5:36 PM, Evan Baker said:

How do you keep the substrate in a planted tank from becoming anaerobic?  Or what causes the substrate to become anaerobic?

 

You can also take a skewer and poke it into the substrate. That’ll help release any gas pockets that might have formed. 

[Streetwise]

Can anyone clarify anoxic vs anaerobic?

[face]

On 8/13/2022 at 5:41 PM, Streetwise said:

Can anyone clarify anoxic vs anaerobic?

anoxic is an environmental thing so substrate is anoxic (no free oxygen) where anaerobic is a biological thing so bacteria in anaerobic (requires no free oxygen) at least that's the  way i understand it in practice both words are used interchangeably.

[Evan Baker]

Ahhhhh..... I mis-spoke.... Anoxic is what I'm trying to avoid.  Thanks for all the input.

I had a tank that went anoxic I believe.  Large pockets of hydrogen sufate or whatever the gas is built up in the gravel.  When I did maintenance on it last weekend removing some plants and stirring up the gravel from it large gas bubbles were released making my entire basement wreak, and my wife very unhappy with me and my hobby.   It was a heavily planted tank and all I had done with it was vac the surface and only occasionally dig in to the gravel in the areas with less plants due to not wanting to disturb the roots of plants.

 

 

Edited August 13, 2022 by Evan Baker

[Streetwise]

I have had some buried gas in my organic soil tanks with substrate layers. I have poked it to off-gas, but I didn’t have side effects. However, I don’t really do water changes, so everything is in slow-mode.