Heater cables providing sediment aeration,powersand providing aeration vs plant roots

Tom Barr

Staff member
Jan 23, 2005
I've long held that plant roots add significant O2 and in conjunction, provide excellent cycling with bacteria.
Unlike cables, plant roots provide extremely high surface area and a wide variety of critical nutrients for bacteria. Powersand has reasonable surface area(any pumic, lava rock, porous clay etc will), but pales by comparison to the fine roots of plants. Some support for this:

Plant roots cycle carbon and nitrogen as much as aeration.
Not bad. If you merely argue for the physical processes, eg, if the system was designed by an engineer, not an aquatic plant scientist, often they tend to leave out the biological component. I believe that this was the case here.
All they looked at was the bacteria and aeration.
Not the plant's role.

Some aquarist have claimed that the plant roots do not do much, but observations and removal and establishment of large root systems seems to suggest otherwise. Few aquarist have ever bothered to use a redox probe in their sediments. Other aquarist having already bought the cables or powersand seem resigned to justify their equipment/products as a "choice", faith based purchases rather than any real evidence or observations that led them to their purchase.
We all do that to some degree(I am no different, but later I do look into it to see).:eek:
I get worried when folks start to assume that the sediment is so simple.
It's not.

It's not this mechanical process of in/out based on thermal convection, or some larger grain sizes on the bottom.
These pore spaces that transfer water in/out clog with time.
And if you have ever seen your filter pad, you know after a week or two in a planted tank, all the leaves and detritus clog things up pretty quick.
Adding all that organic matter down into the sediment causes the bacteria to mineralizes the organic matter. This oxidizes the reduced carbon, and gives the bacteria energy and gives off CO2, just like us.
As the O2 declines due to this, the bacteria have little O2, so they start going after Fe and NO3, but this is a much slower process.
After some time has past and excellent plant growth has sent the roots deep into the sediments, the bacteria are once again supplied with O2 via the roots and can now process most any waste and mineralize it rapidly.
Once the roots are established and you do not remove and uproot too many plants at one time(a good rule of thumb is never uproot and remove more than 1/3 of the tank at a time), the tank will run much better and cycle well.
To date, I've never had any sulfur reduction or bad anaerobic conditions in any sediment I've used(25+ years of growing plants and 15 years for CO2 enriched systems).
I have also used ADA aqua soil without any powersand for several years now and never once had any related issues due to a "lack of flow", anaerobic conditions or anything I could suspect or relate to the low O2.
I think most aquarists have noted that a simple test to see how something works and if it's relevant/important/critical to plant growth/health, is rather simple:
Turn the heating cables off/on over say several months time blocks.
Note plant health/growth, sediment appearances for anaerobic condition etc.
For ADA: same type of thing, add it and then do not for another tank.
Make the same comparisons (you will need to account for nutrients as PS does have some NO3 in it and peat, so you will want to add non limiting nutrients to both the ADA AS and the ADA AS+PS treatments).
This is not high grade research science, this is simple farmer style common sense.
Some more:

Main points here are that the sediments can re release nutrients back into the water column, hardly a nutrient limiting method over the shallow ands small volumes that our tanks have. Further, the loading rates of detritus in your tank has a strong influence on the sediment and it's O2 level.
Power sand or cables will not regulate that over time.
It'll just clog faster.............or not and then it will not matter either way.

http://wetlands.ifas.ufl.edu/publications/PDF-articles/173.Nutrient transformations.pdf

Note, many of the test look at things over time, not once has this been done with cables or PS.
As organic matters builds up over time and given that it, and nothing else is the driver of anaerobic, low O2 conditions in the sediments, why was this not looked at? Both with and without plant roots?
These are common sense logical test to show whether or not heat cables or any larger grain layering(what happens to the smaller grains of aqua soil, detritus, or when you uproot to these large spaces over time?) play any role.
Some have argued that they help "start a tank", the time period between plant root establishment and a new tank without any plant roots.
This argument at first appears to have merit, but it's missing one very critical part: you still need some source of organic matter down there and the time for it to accumulate!
No organic matter for the bacteria (oops, BTW you need a good established bacterial colony as well as the organic matter!) to use , then no depletion of O2.
So you need the organic matter source and enough to keep things really low for O2 as well as an established bacterial community.
Neither of which are present in a new tank. Everything in any aquatic sediment is defined by the carbon loading(reduced carbon, like carbohydrates, sugars etc, the stuff you eat as well and the same things plants use for energy and leach out into the sediment slowly).

You cannot ignore this and try to argue anything about aquatic wetland sediments with aquatic macrophytes.

Tom Barr

Tom Barr

Staff member
Jan 23, 2005
A good primer on anaerobic soil:
http://wetlands.ifas.ufl.edu/publications/PDF-articles/Anaerobic Soils.pdf

This is also an excellent paper:
http://wetlands.ifas.ufl.edu/publications/PDF-articles/224.Regulation of organic matter.pdf

Also a great read:

http://wetlands.ifas.ufl.edu/publications/PDF-articles/253.Carbon and Nitrogen.pdf

Anyone thinking they can limit algae via PO4, this paper cites as well as others, a less than 10ppb, that's billion, are common ranges in the everglades where there's a lot or periphyton.

http://wetlands.ifas.ufl.edu/publications/PDF-articles/Biotic and abiotic uptake.pdf

CaCO3 appears to be fractioned into 15% of the PO4 added, and 85% or so is taken up by algae. So the precipitation of PO4 does occur, but a lot of it ends up in the algae.

Tom Barr