Bio-Glass vs. Eheim Ehfisubstrat..? and why?
- Thread starter RDTigger
- Start date
Bderick67;3244905; said:
As you may recall, one of Archimede’s greatest achievements was to prove that a sphere has 2/3 the volume and surface area of a comparably sized cylinder. So, we already know that cylinders will have greater surface area than similarly sized spheres. We can calculate the surface areas for spherical and cylindrical particles. The average diameter for an Ehfisubstrat Pro spherical particle is approx. 7 mm (0.7 cm). We can compare the Substrat Pro sphere with a hollow cylinder having comparable dimensions. Let’s assign this cylinder a height and diameter of 7 mm and a wall thickness of 2 mm.
First, the surface area of the Substrat Pro spherical particle is calculated by 4pr2. [4 x p x 0.352] = 1.54 square centimeters. Bear in mind that this is only the “gross” surface area. Most of the sa is provided by the texture of the material. The texture is a result of the specific material from which the particle is made. In this case, sintered quartz. The actual or “theoretical” surface area could easily be 1,000x the gross surface area because of all of the little nooks and crannies provide by the surface texture.
For a cylinder, the surface area is calculated by [2pr2]+[2prh]. However, since this is a hollow cylinder with additional surface area on the inside and an open top and bottom, we have to modify this formula. So, the overall equation for our little cylinder is:
[2 x p x 0.35 x 0.7] + [2 x p x 0.15 x 0.7] + 2[(p x 0.352) – (p x 0.152)] = 2.82 square centimeters. Of course, cylinders with different dimensions would exhibit different gross surface areas.
These figures indicate that if we compare the gross surface areas of a sphere and a hollow cylinder which occupy approximately the same amount of three-dimensional space, the hollow cylinder would be expected to have almost 2x the surface area…but ONLY if they are made from the same material. Assuming they were made from the same material, does this mean that if we were to scrupulously compare the performance of these spheres and hollow cylinders as biofilter media, that you could achieve an identical effect by using half the number of cylinders? Probably not. The reason is that there is a substantial difference between “theoretical” surface area and “accessible” surface area. In other words, the surface area of a biofilter particle is only useful if moving water can be brought into contact with it.
A spherical particle optimizes the uniformity of water flow through the particle bed and ensures maximal contact between the water and all of the particles within that bed. In a spherical particle bed, water flow is the same, regardless of where it occurs within the bed. Such uniformity is only possible with a spherical particle. The scientists at Eheim certainly knew this and that’s why Ehfisubstrat Pro particles are spherical. In contrast, non-spherical particles (like hollow cylinders) can arrange themselves in many different orientations and hence, water flow across (and through) non-spherical particles is much less consistent. For example, if the end of a hollow cylinder comes to rest against the side of another cylinder, then water will not flow through that first cylinder. Consequently, that internal surface area is underutilized. Also, if two cylinders come to rest side-by-side, they essentially form a barrier to water flow, etc. So, non-spherical particles form media beds with highly inconsistent flow patterns, in which much of the surface area is utilized suboptimally because it is not fully exposed to water movement. To what extent other factors, such as turbulence, compensate for this lack of uniformity in water flow is difficult to determine.
The other issue to consider is particle diameter. Smaller particles have a higher surface-to-volume ratio and that’s a good thing if you want to colonize bacteria. However, smaller particles also pack more tightly and impede water flow through the particle bed….and that’s not so good in a canister filter. Spherical particle diameters have to strike a balance between maximizing surface area, but not packing too tightly. I assume those considerations were taken into account by the scientists at Eheim and are reflected in the particle diameter range of Substrat Pro. Irregularly shaped particles (like cylinders) pack in a completely chaotic manner within the bed…some areas are tight, some are loose and some are in between. Again, this means that water flow through the bed is non-uniform.
In actual use, my impression from talking with many aquariasts and reading many posts is that the non-spherical media types, nonetheless, seem to provide sufficient surface area to assimilate ammonia and nitrite. This is probably because even though their sizes and shapes are much less efficient, the volume of media used provides enough surface area for the requisite number of bacteria. There may also be compensatory factors, such as turbulence. Media beds comprised of non-spherical particles would be expected to generate much more turbulence and this additional mixing within the bed could allow for additional contact between the water and the particles’ surface. So, although a spherical particle shape is more efficient than other particle shapes, when loaded into a canister filter, the end result is probably going to be indistinguishable in terms of ammonia and nitrite readings. However, if I had my choice, I would go with a spherical particle every time. In fact, I use Substrat Pro exclusively. If cost is not an issue, my feeling is that you will always give yourself an edge by employing a spherical particle with a high surface area and optimized particle packing.
There's a sticky, I think in the DIY section, that speaks to the surface areas of the various filter materials.
nice post brian...
I was thinking about that principle. The hollow cylinders would have more surface area than the regular efsubstrat i picked up on clearance...
The Pro was $30, I got a a liter of the reg stuff for $14.99. It is not the best for flow rates but was trying to figure out if the Bio-Glass hollow cylinders would be as good/better than the irregular shaped Efsubstrat. Went with the Eheim stuff but I know I can't go wrong with either one.
I was thinking about that principle. The hollow cylinders would have more surface area than the regular efsubstrat i picked up on clearance...
The Pro was $30, I got a a liter of the reg stuff for $14.99. It is not the best for flow rates but was trying to figure out if the Bio-Glass hollow cylinders would be as good/better than the irregular shaped Efsubstrat. Went with the Eheim stuff but I know I can't go wrong with either one.
