Adam Gottschalk wrote in message ...
In "A practical guide to choosing your aquarium plants", Peter Hiscock
advocates letting one of the sponges in a canister filter clog up so as
to allow for anaerobic bacteria to develop there, as a complement to the
anaerobic bacteria which are (hopefully) building up in the substrate.
For the same reasons, he advocates a flow rate of half the typical
recommendation. He writes, "The ease with which water flows through
[medium/large-grade inert gravel] substrates will remove nutrients,
create oxygen-rich conditions, and cool plant roots, all of which will
severely hinder plant growth." Obviously, he is a strong advocate of
substrate heaters. Published in 2001 by Barron's. I think it's a solid
book. How do the above assertions sit with various folks' experiences?

For a CO2 enriched plant tank and in general:
I would never suggest you to let your filter clog. Mainteance is a key
to keeping aquariums. Canisters can long peroids without cleanings,
but generally removing mulm and organic build up is a good thing. He
does mention large to medium gravel, well that's not the best for
plants anyway. 2-3mm or specialize substrates are much better such as
flourite, onyx sand, etc.

As far as bacterial cycling, substrates are where roots exist. Roots
need O2, they release O2 if the surroundings are anaerobic. Roots are
not static nor is the substrate. Plant roots do not need anaerobic
condition to thrive. This is a MYTH. I can say this because I've grown
many plants in very aerobic conditions and so have many hydroponic
growers which is one of the main methods for aquarium plant
culture....but the nutrients are generally in the water column with
these methods.

Cooling of plant roots has never caused an issue for me in decades,
cables have never once been shown to help significantly(anyone's tank,
where the improvement was due to cables alone)nor anecdotally with my
own tanks(I've had 7 cable tanks over the years for long peroids),
some might claim subtle differences, but they would be subtle at best.

O2 rich environments in the roots do NOT severely hinder plant growth.
I discussed this years ago about RFUG's and my tanks which at the time
did much better than those with cables(which I also had)or their no
flow systems(no cables/RFUG's etc)See APD.

Using a substrate like flourite which has high surface porousity both
externally and internally in each grain, plenty of trace metals like
Fe, Mn will yield a much more significant and better improvement for
your plant growth.
This way the roots get the O2 they need easier, but also have the
advantage of the anaerobic internal spaces in each grain.

Uprooting etc does not cause problems for the bacteria since each
grain is it's own unit and environment.

Filter's are mainly for mechanical removal of detritus, water
movement, back up for plants in case they get stunted.

My vote would be to clean the filter or use a filter that removes fine
particles. Alternatively, large weekly water changes will also keep
this down.

Non CO2 planted tanks are seldomed cleaned, but half clogged filters
are not why those work well. Stable flow rates will help, a half
clogged filter is waiting to become totally clogged.
Simply reduce the flow rate itself if that's the goal. There's plenty
of bacteria in the substrate already and keeping the flow rate stable
would be more helpful to the cycling in a tank.

Regards,
Tom Barr