The "Geosapper" Feeder (Surge Feeder)


This design is being released in Reefkeeping Magazine as a service to the readers of Reefkeeping. By releasing this idea/design here for the public to see, it now becomes public domain. This means YOU can make one or have someone make one for you. In the interest of sharing information, if you see room for improvements or additions for more functionality, please post them for public use.


As is the case with most things in life, the reefkeeping hobby is always seeking ways to advance and improve. One area in particular where improvements have been sought is in providing food sources more appropriate for reef tank inhabitants, namely, live foods. This interest in providing live foods has brought its own set of challenges (or opportunities, depending on one's viewpoint). The first challenge to be met was to develop techniques to culture live food and insure the quality (and quantity) was significant to warrant the effort. In the last couple of years we have seen articles, websites, and discussion boards devoted to educating the reef keeper on the basic, and sometimes advanced, methods of culturing live foods. The term 'live foods' has grown to include brine shrimp, rotifers, ciliates, copepods, and numerous microalgae with each having specific benefits for the food chain we try to mimic.

So let's pretend that we know all we need to know about culturing live foods. Wow, we got real smart, real quick! But this brings us to the next challenge in reef keeping, to wit, "How do we get the food into the tank?" Sure, we can dump some food in the tank every evening. This works, and works within acceptable terms. But is there a better way? Is there a way to incorporate 24 hours/day, seven days/week drip-feeding? Is there a method that doesn't require the aquarist to carry three bottles of different cultures to the tank everyday? The answer is maybe, just maybe.

If we look at how reefs in nature feed, we might find an answer. Natural reefs are fed by the tides surging food onto the reefs. With every surge, food is swept over the reef. Already, some reef keepers are applying surge type movements for current. What if we could use this same idea to feed the tank? What if we could provide an almost constant supply of food to the tank in surges or small 'prescribed' doses? It would really be a benefit if we didn't have to stand there and manually apply each feeding to the tank.

Well, I thought it was a good enough idea to spend some time thinking about how this might be achieved. After spending a little time considering the possibilities, I developed an idea that has worked quite well. This idea required the use of acrylic. Not being gifted in working with acrylic, I enlisted the expertise of George Weber of to give me a hand with the construction. I showed him the drawings for this new idea. We discussed it back and forth and the outcome, looking somewhat like the result of a cross between a skimmer and calcium reactor, was the "Geosapper" feeder.

click here for full size picture

While looking a little complex at first glance, the "Geosapper" has proven to be well worth the effort. A major benefit to the "Geosapper" is that it contains no moving parts. The only maintenance after initial setup is a periodic cleaning, which is easily accomplished as each section comes apart by loosening a few screws.

The "Geosapper" can operate without moving parts because of the integration of small surge devices. So, in order to understand the operation of the "Geosapper", we need to understand surge devices. Surge devices work on a siphon. Water fills the container, and when the water level reaches a point higher than the highest point of the surge tube, the water is siphoned out. The siphon continues until enough water has been removed that a siphon break occurs. This stops the siphon (surge) and allows the container to refill before surging again.

With a basic understanding of surge devices, the best way to describe the operation of the "Geosapper," is to break it down into its three distinct sections:

Top Section - Phytoplankton, Middle Section - Rotifers, Copepods, Ciliates, etc..., Bottom Section - Brine Shrimp. (The brine shrimp are in their own, and last, section because they tend to eat any and everything they encounter).

Top Section

The top section is nothing more than a holding station for phytoplankton. Fill the top section with phytoplankton, easy enough. The choice of species or type of phytoplankton is purely up to the user. Each section is equipped with an air bubbler to maintain a high quality of live food. There is an option to use two different types of phytoplankton, but we'll discuss that in the section below. From this area the phytoplankton then drips into the middle section via a drip valve.

click here for full size picture

The drip valve is the key to proper operation of the "Geosapper." The drip valve regulates the flow rate into the middle section. The importance of this valve will become more clear as I proceed. The picture to the left shows the drip line with the inline drip valve connected to the top section. The installation of the drip tube makes adjusting the flow rate very easy. With the end of the drip tube above the water line of the middle section, each drop can be observed. This is critical to ensure the proper flow is set.

Middle Section

The middle section houses a batch of rotifers, copepods, ciliates, etc. For the purpose of this article we assume we are only using rotifers. As the phytoplankton is dripped into the middle section from the top section, the rotifers are fed and allowed to multiply. Once the level in the middle section reaches the surge point (a level just above the surge tube), a predetermined amount of phytoplankton and rotifers are surged into the bottom section. The surge leaves behind enough phytoplankton and rotifers to allow the continued reproduction of the rotifers. In most cases this is enough to sustain a continuous culture for a long time period. This is ultimately determined by the size of the actual "Geosapper" and the size and frequency of the surges.

click here for full size picture

The surge tube can be seen in the middle of the picture titled "Middle Section". Also, towards the bottom of the middle section, the air bubbler can be seen. Again, the air bubbler ensures oxygen distribution in the water and provides a low, steady current to keep the contents of each section in suspension. The middle section has an addition of a fill/vent tube. This is PVC tubing which runs from the middle section to the point just even with the top section. The fill/vent tube is used to restock the rotifers (should it be necessary) without having to take down the entire unit. The fill/vent tube also allows air to enter and leave the section for proper surge performance.

Bottom Section

click here for full size picture

The bottom section is used to house freshly hatched brine shrimp. The brine shrimp will load up on the phytoplankton and rotifers being surged in from the middle section. This surge from the middle section raises the level of the bottom section, thereby causing another surge action to occur. This last surge takes phytoplankton, rotifers, and brine shrimp into the tank.

The picture on the left shows the air bubbler, fill/vent tube, surge tube, and the output to tank.

The unit in operation. Green food coloring was added
to the water just for purposes of the test.

Additional Tidbits

Drip Rate

The adjustment of the drip valve flow rate controls the frequency of the surges. A faster drip rate equates to a more frequent surge or more food into the tank.

Surge Amounts

The surge amounts are determined by the size of the surge tube. The shorter the surge tube, the less the amount that will be surged.

Using Two Types of Phytoplankton

The top section has an extra connector in the middle of its base. This can be used to connect to another drip line for a different type of phytoplankton without having to mix them in the top section. This will allow two distinct types of phytoplankton to be fed to the middle section and then surged through the "Geosapper."

Sizing the "Geosapper"

For the unit pictured here, the total volume is approximately one gallon. The Top Section holds approx. ½ gallon of phytoplankton and each of the other sections holds approximately one quart. The acrylic tubing used for each section can be larger in diameter and length to accommodate larger applications.

To determine the appropriate size for your application, we need to know how to calculate the amount of the surge. For example: Using a 8" acrylic tube with a 0.5" surge tube, we can calculate the volume using the formula (pi)(r^2)h, "r" is the radius of the tube and "h" is the length of the surge tube. So, our example is 3.14*16*0.5 = 25.12. Then we take that number and divide it by 12^3 (12^3 = 1 cubic foot). We now know we have 0.014 cubic feet of surge. Since 1 cubic foot equals 7.5 gallons, we see 0.014 * 7.5 = 0.10 gals or 12.8 ounces.

Knowing each surge is 12.8 ounces and the top section of the "Geosapper" holds 64 ounces, we can calculate the number of surges per fill of the top section. This is done by dividing 64 by 12.8. This gives us 5 surges per fill.

To change the amount of each surge, we simply change the diameter of the acrylic tube or the size of the surge tube. We can also change the size of the top section to adjust the maximum number of surges per fill.


The top section could be filled with salt water, the middle section left empty (with Surge Tube removed), and the bottom section filled with brine shrimp or other suitable live food. Using the "Geosapper," one could surge feed live food to seahorses to provide constant live food.


Because we are adding saltwater to the tank, care must be taken that the salinity of the tank does not change drastically. The easiest way to accomplish this is to remove the same amount of tank water as the amount of phytoplankton added to the top section of the Geosapper.

If you have any questions about this article, please visit my author forum on Reef Central.

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The "Geosapper" Feeder (Surge Feeder) -