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re: Heating Coils revisited
From: Erdoz1 <erdoz1 at wt_net>
Date: Sun, 02 Jul 2000 22:18:02 -0500
Just when a post shows up that I want to answer, my home PC goes belly up!
Go figure. Maybe my newly spun-off employer will give me a personal e-mail grace
period while my ex-employer takes its sweet time with the warranty repairs on
the PC it sold me.
>Could a modified under gravel filtration plates serve the same function
>as the under gravel heating coil systems?
>Take an UGF plate with a slightly longer than normal return tube that
>rises about 1 cm above the normal level. Supply water into the return
>tube (from the filter outlow) so its serves as a constant overflow weir
>to impose a very slight static head. This would result in a very small
>reverse flow through the substrate, duplicating (what I understand to be)
>the primary benefit of heating coils - providing enrichment to the
>root system and avoiding totally anaerobic conditions by creating a very
>small small circulation pattern from the water column through the root
In theory, such a setup should provide almost all the supposed benefits of
heating coils - minus the heat, of course. Nutrients added to the water column
(naturally or otherwise) would be carried into the substrate. If the substrate
has something in it to bind the nutrients (clay-like additives, for example),
the nutrients will be held in the proper state for plant roots to adsorb. A very
slow flow will not bring too much O2 into the substrate, maintaining a reducing
However, heat IS one of the benefits of coils. Besides helping those few plants
that like "warm roots", it also increases the rate of biological processes in
BUT (and that's a "big but" in case you didn't notice), in practice a very slow
reverse flow may be difficult to achieve. Water, like electricity, takes the
path of least resistance. In all likelyhood, all of the slow flow will find some
channels in the substrate near the downlift tubes (or will make some over time)
and simply escape via those routes, leaving most of the substrate devoid of
circulation. In other words, it will be very difficult to generate a slow flow
through the entire substrate.
Futhermore, consider how much flow is needed in the downlift tubes to produce a
slow flow in the substrate. Let's try a hypothetical example (hypothetical since
I [nor anyone else?] don't have a clue as how much flow a proper heating coil
Let's take an 85 gallon aquarium with a footprint of 17.5" x 59.5" (such as one
I had at one time), giving a substrate surface area of roughly 1040 square
inches, or more conveniently, 6700 sq. cm. Let's also say we wanted a flow rate
through the substrate of 1 cm per hour (I picked that because it doesn't sound
like much). That is, a particular molecule of water would travel 1 cm in 1 hour
and would travel from the bottom to the top of the substrate in around 7 hours.
I'm making a leap here so please correct me if I've run afoul of science and/or
common sense, but that flow "speed" seems to correlate to 6700 cubic cm per hour
or about 110 cu cm per minute.
Lift tubes are, what, 1" in diameter? Assuming that is correct, each lift tube
has an area of about 5 sq. cm. Assume 4 tubes in an 85 gallon aquarium or about
20 sq. cm. total area. To get 110 cu cm per minute (leaping again), you need a
flow speed in the tubes of about 5 cm per minute. That would seem pretty fast to
be generated by a 1cm head, as mentioned above.
Whether or not my example makes sense, the flow down the tubes is faster than
the flow in the substrate by the ratio of the total tube area to the total
Food for thought.
George Booth in Ft. Collins, Colorado (booth at frii_com)
Web site still active even though the old PC is not: