Copyright 2000 by George and Karla Booth
Decisions, decisions, decisions. In the process of selecting equipment for a new aquarium, the aquarist is faced with a bewildering array of choices. Alternatives such as a glass or acrylic tank are mostly decided by availability or price. The type of filtration is sometimes dictated by the requirements of the tank inhabitants but the decision can be very confusing for a newcomer. Luckily (or unfortunately, as the case may be) there are usually lots of opinions and advertising claims available to help this decision.
Sometimes, selecting the right alternative is very difficult. We were faced with such a decision when we went about setting up a new, 330 liter, heavily planted discus show tank three years ago. We had applied some of the high tech ideas presented in "The Optimum Aquarium" (Horst and Kipper, 1986) to an earlier 300 liter gallon planted aquarium and were very excited by the result. We felt that getting closer to the ideal "optimum aquarium" would produce even better results and would be beneficial to the delicate discus we intended to keep.
The toughest equipment decision was whether or not to use undergravel heating coils. Undergravel heating is a relatively new concept in North America, and we didn't have much information pro or con. "The Optimum Aquarium" stressed the importance of the coils but didn't provide much background or scientific information concerning WHY they were important.
We made some educated guesses about what they did and how we could achieve the same effect with lower cost alternatives. We finally decided not to use them and set the aquarium up with a gravel and laterite substrate with no mechanical means of water movement through the gravel. We felt that a large population of Malaysian burrowing snails combined with healthy, well-rooted plants would provide enough substrate activity to prevent dangerous anaerobic areas from forming. This turned out to be the case, but we were unaware of another, more important function of the coils.
The rest of this story is how we discovered "the truth" about the heating coils and how important it is for hobbyists to have open discussions about various aspects of aquaculture. It also illustrates the value of computer forums such as "Fishnet" on Compuserve and the "aquaria" conferences on Internet in getting together people of diverse backgrounds to help each other understand their pursuits more thoroughly.
Once we had the new aquarium set up, we described what we did on the Internet computer network. The responses to the posting were quite complimentary with the exception of one gentleman. He was quite surprised that we chose not to use substrate heating coils, and, at the urging of the network participants, gave us a good education on the real benefits. We feel that his comments are very worthwhile and want to share them with the readers of Aquarium Fish Magazine.
Unfortunately, we have lost contact with this contributor, Jeff Frank, so his comments are paraphrased, edited and reprinted without his knowledge. Perhaps he will see this article and continue the dialog with us at a future date.
For those unfamiliar with Internet conventions, the |
following will help readers understand the discussions:
> (author) writes:
The ">" indicates quoted text from a previous discussion
to serve as context for the current entry.
Also, to save typing, the book "The Optimum Aquarium"
is sometimes referred to as "TOA".
Now, on with the story.
From: (Jeff Frank
Date: Tue, 14 Aug 1990
> We have set up a new 100 gallon aquarium following "The Optimum Aquarium"
> very closely. We have done everything except the substrate heating coils.
I'm curious as to why you would go through the expense of setting up an "almost" optimum aquarium. The laterite and the heating coils are intimate components.
Visualize if you will a biotope of your choice. In your mind take along your 100 gallon tank. Imagine that it does not have the bottom in place, just the 4 sides. press this into the SOIL of your biotope so that the you will have 3 inches from the top of the soil to the bottom of the sides.
Carefully slide in the base from a side so you include the soil. Let's just say the bottom is now fused again to the sides so we have taken a piece of nature, straight out of the biotope, including water, soil, plants, fish, etc. A perfect scenario? Nope. It does not take a expert on ecology to see that less than optimum plant and fish health will result, even in natural light.
What has happened is that the movement of water through the soil substrate has been blocked. Plant roots need oxygen to metabolize. There is a soil substrate/water/root hair interface of tremendous import that is disrupted.
The authors of "The Optimum Aquarium" tell you the coils are there to supply slow steady convective movement through the substrate. In my opinion, this is the only method on the market which provides water movement slow enough to keep the laterite in place.
The laterite in the substrate serves a critical function in a planted aquarium. The laterite has many negatively charged sites; ammonia in the form of ammonium ions is positively charged. The laterite attracts and holds the ammonium ions like a magnet until a plant root hair exchanges another positively charged ion for the ammonium (adsorption) and takes it in to metabolize into amino acids and ultimately protein. No laterite, no negative charges, no easy ammonium uptake.
You have the additional benefit of removing ammonia. Instead of just the "ammonia to nitrite to nitrate" cycle in biologic filtration, you will bypass the "nitrogen cycle" and its accumulating nitrate level. The nitrogen ends up being removed from the tank as you cut and prune excess plant tissue because plant tissue is partly made of protein, which is 14% nitrogen.
Just as important is the understanding that in nature, streams and ponds are the intersection of a topography where groundwater intersects the surface. This means water is constantly moving one way or the other, into or out of the water body proper. Your 100 gallon tank sunk into the soil has cut off this exchange process. You don't have the ecological marvel you thought you had since oxygen and ammonium can't circulate through the soil substrate.
The scientists at Dupla figured out that since you have to heat the tank anyway you might as well do it by putting a coil in the substrate. The gentle currents emulate the ground water/surface water movement. It isn't just that the roots like to be warm. Some experiments on terrestrial plants show marked increase in growth if you heat the soil higher than the surrounding air. I don't think you would see as much of a response in aquatic plants. Rather, reduction reactions (those which make nutrients more soluble, and thereby more available to plant uptake) will take place at an accelerated rate (2-3 times faster for each 10 degrees C rise in temp) but this will show up only when any nutrient is limited.
One thing I have considered is that I think the coil in the substrate becomes less and less important as healthy plant roots fill the substrate. The laterite remains essential because of the positive/negative ionic attraction, but after the substrate is a mass of roots, the pull of water as it moves up through the plant will draw tank water with fresh oxygen and ammonium down into the substrate. I have difficulty seeing how you can keep the oxygen and ammonium levels, much less the less mobile nutrients like iron, adequate in the root zone during the initial phase without the substrate heating coils.
I am looking forward to your reports. You are ahead of many by managing the CO2/carbonate chemistry. I have no doubt good things will result. If you understand what I've detailed you will see how things can be made more optimum.
Date: Fri, 17 Aug 1990
Jeff, thanks for the well thought out response. It's nice to see someone out there in netland thinks the optimum aquarium stuff is worth pursuing.
I have some conceptual problems with the heating coils. In theory, they sound great - warm water rises and cold water comes down to take its place and you get wonderful circulation. But, in practice, the concept seems full of holes - literally. Let me draw a picture:
+-----------------------------------+ | | | | | -----------------------------00 | | | | / | | | coils -+ | | \___________________________ | | | | | | \ | | | v | | ___________________________/ | | | o o o o o | | / | | +--------------------------+ | \___________________________ | | | \ | | cross section | ___________________________/ | | | / | | <- top view | \_____________________________/ | | | +-----------------------------------+
Based on the picture in the "TOA", the heating coils are spaced an inch or two apart and do not go all the way to the sides or end of the tank. It seems clear to me that there will be a lot of areas ("holes") that do not get the benefit of the convection currents, causing potential anaerobic patches. I would also suspect that the currents will channel to the paths of least resistance, especially around rocks and driftwood, so that some areas get less circulation than others. Also, I infer that the controller will keep the water temperature to within a few tenths of a degree from the set point - how much convection will occur with that small a differential?
We wanted to try heating coils but the few doubts we had coupled with the cost dissuaded us from doing it. Hopefully there are two mitigating circumstances that will prevent problems. We have a large population of Malaysian snails that burrow in the substrate during the day, preventing bad things from happening in the gravel by areating it. Second, almost all the plants we started with are from our other tank and had decent roots. We did some rearranging this weekend (7 days after setting up) and found amazing root growth. So if you are right about the coils being important just at first, maybe we will get lucky.
I was intrigued by your discussion of ammonia/ammonium in the laterite. Do you have a source so we could do some further reading? My wife is a biochemist and likes to get down to the nitty-gritty on this stuff. I'm just an electrical engineer, so concepts like "use warm clay under the gravel" keep me satisfied!
From: (Jeff Frank)
Date: Fri, 24 Aug 1990
> I have some conceptual problems with the heating coils. In theory,
> they sound great - warm water rises and cold water comes down to take
> its place and you get wonderful circulation.
The Dupla coils work well because they work like a campfire, with regard to convection. Heat will cause water around the coil to become less dense. Most of this water will rise straight up from the coil. Cooler, less dense water will be drawn in from between and under the coil. A coil placed directly on the bottom pane will not be as efficient as one stood off a bit. It is true that there is a spacing between coils, which when exceeded, will result in inadequate flow in these middle spaces. I hope you can see the opposite is also true. For a given water volume, coils spaced too close together will minimize the effect.
> I was intrigued by your discussion of ammonia/ammonium in the laterite. Do
> you have a source so we could do some further reading? My wife is a
> biochemist and likes to get down to the nitty-gritty on this stuff. I'm
> just an electrical engineer, so concepts like "use warm clay under the
> gravel" keep me happy!
It is not ammonia/ammonium in the laterite. Laterite, or any clay for that matter has a crystalline structure which has negatively charged sites. Ammonium, or any other positive ion is attracted by the negatively charged sites. There are no negatively charged sites to speak of anywhere in the aquarium, except decomposed organic matter, unless you provide laterite.
Laterite is a highly weathered remnant of volcanic rock (weathering implies exposure to tropical temperature, precipitation, and forest derived humic acids over geologic time). Soils from temperate regions not exposed to the accelerated weathering of the tropics retain too much Ca++ and Mg++ which will adversely affect hardness and pH in a plant tank.
The heating coil provides just the right velocities to circulate the tank water with its ammonium throughout the substrate. Some of this is exchanged for H+ (protons) or other cations (positive ions like K+, Ca++, Mg++, Na++, Al+++).
If other plant growth factors are present in reasonable amounts, we will have good root growth. By good root growth, I don't mean lots of roots. You can have hardy plants with big thick masses of roots in other systems. I mean here root hair proliferation. Only under the special conditions including substrates relatively high in cation exchange capacity and oxygen content can the tremendous surface area and nutrient adsorbing power of root hairs be optimized in an aquarium. (Adsorption is the direct exchange of a nutrient cation such as NH4 from an exchange site on a substrate for a H+ from H2(CO2) from a root hair) Plants in other systems have no cation rich substrate for roots to exploit, so don't mass root hairs. They are less efficient. Plants in these other systems can do quite well taking nutrients up from the water by absorption. (Absorption is the drawing in of nutrients as the plant draws in water.) Higher plants have developed vascular systems which prefer to adsorb through roots.
From: (Jeff Frank)
Date: Tue, 4 Sep 1990
> I'm not saying I don't think the coils work well. I just hope there
> may be other ways to achieve an optimum aquarium without some of the
> expense. I'm just not convinced that heating coils are the ONLY way
> to go. Dupla's arguments against under gravel filters don't seem very
It is my view that healthy aquatic plant roots preferably ADSORB cations to the ABSORPTION of the same. Undergravel filters (UGF), even reverse flow undergravel filters (RUGF), by definition force water through the substrate. This is like trying to administer a flu shot with a fire hose. When discussing nutrients like nitrate and phosphate (these are anions) one speaks of "mass flow". Mass flow is the movement of ions at the same rate at which water moves through membranes into the plant. These anions are ABSORBED by higher plants (those with roots) and lower plants (more primitive plants like algae) alike. The trouble is, if anions were to be taken into a plant without cations in equivalence, any plant would suffer from a fatal pH swing (protons, or H+ will be required to satisfy the negative charges of the anions, thus increasing acidity). While anions bounce around with protons in solution, most cations plants are interested in are insoluble, or only slightly soluble.
To remain alive, a plant (or any organism) has evolved safeguards to protect tissues from too much (toxicity), or too little (deficiency) of any given substance. These safeguards are imperfect. In some instances, they just weren't designed to handle situations we aquarists invent (or provide by neglect). It might have been luck or design, but somebody hit on the fact that water movement as supplied by UGFs was too great to let roots do their job. The bane of UGFs is that water will seek the path of least resistance. An advantage to a wire in a serpentine pattern throughout a substrate is it puts the slow convection currents pretty much everywhere. This convection approximates the flow of water by gravity (percolation) through the substrate. If you insist a UGF is better because it moves more water and therefore more nutrients, you still haven't grasped the difference between ADSORPTION vs. ABSORPTION, or equilibrium between anions and cations (remember living tissues are about neutral in pH, even when the outside world is acidic or alkaline, therefore total negative charges, or anions divided by total positive charges, or cations must equal 1) and I can't think of a better way to put these important concepts.
As I write this, I realize this topic is like discussing religion. Strong beliefs die hard. If you are easily converted you probably are naive, or you just like the minister. If you aren't easily converted you might be just stubborn, or you might be right. Most of the time you just go on believing your doctrine and I go on believing mine. In this case, it looks like you carefully researched things and just decided you could spend $30 on a submersible heater instead of $350 on a substrate heater. I bet you never thought someone that only keeps killifish and java moss, and uses no filtration or lighting, would say you didn't quite spend enough money.
There sure doesn't seem to be a middle ground.
Continued success to you,
The end result of all this discussion was to convince us that substrate heating is critically important in a thriving planted aquarium. In our case, the aquarium did very well without the coils for the first year and then has shown a gradual decline. We attribute this to the lack of a mechanism to resupply the laterite in the substrate with nutrients. The plants are still growing nicely but don't seem as robust as they used to. Also, the tank was algae free for the first year but now shows signs of susceptibility to algae.
Based on these discussions, we established another 300 liter, heavily planted aquarium two years ago. This set up has the benefit of heating coils and has maintained it lush appearance and has been algae free for close to two years with no signs of any deterioration. This "Super Show Tank" (SST) set up was described in the four part series "Modern Aquascaping" (Aug, sept, Oct and Dec 1992 AFM)
With the excellent results we have seen the the SST, we are planning to retrofit a heating coil system into the 100 gallon as soon as time permits.
We hope that this article has shed some light on some of the mysteries of aquatic plants and will help you be more successful in your aquatic gardening adventures.