As more and more organic materials, sources of carbohydrates and less labile forms, are degraded via oxidation(thus consumes O2) by bacteria, what happens to the sediment over time?

Are the bacteria more able or less able to consume NH4 and convert it into NO3?

Clearly less able.
What about loading more organic carbon and dead plant materials?

Clearly, again, less able.

This is what is meant by an old sediment/substrate.

It's not so much the accumulation of toxicants etc, it's just over loaded, and no O2 can get down there. So the cycling of waste from above slows down, some times a great deal.

Now.......this is more complicated than this simple system.

1. We have plants roots, sometimes massive root systems growing down there.
These pump large amounts of O2 into this low O2 system and increase and enhance the cycling rates.

2. We uproot and replant, vacuum, remove and minimize the loading rate.
This removes the waste and opens up the pore spaces, that had been clogged prior. We also remove the roots, so that part is a negative. But they tend to grow back pretty fast.....

3. Many tanks have little issue with loading rates, some tend to have a lot.
Depends on the feeding, the plants and their health(ya think??!!), driftwood and sediment grin sizing.

You cannot suggest one size fits all here, heating cable folks love to suggest that, but that is a huge pile of Bovine male manure.

Always has been.

By increasing the rate of flow between the sediment and water column, the effect is that it clogs faster is all. Once the pore spaces are clogged, the rate of flow goes way down. All it does in speed up the clogging.
RFUG's flow rates are high enough to prevent that clogging.
Even these can be clogged if the water is not prefiltered prior.
The sand bed acts as a giant sand filter with heat cables and normal no cable set ups. And like all filters, they clog.

The main issues are listed above concerning sediments (1-3) and clogging.

Regards,
Tom Barr




We also uproot and vacuum every so often.