Central Filtering For
Raising Fry

by Jim Cormier

Four years ago, Henry Debruyn of the Suncoast Killifish Society (Tampa/St. Pete, Florida area), was showing us a filter that he had made and uses on his tanks in his home in Belgium. He gave a couple of presentations at our local club on how it worked and how to build one and I became very intrigued. It was made using a section of vinyl gutter. The gutter is then filled with lava rock and sits on top of the aquarium. It is a typical airlift system to get the water to the top of the filter, and then gravity pulls the water down over and through the lava rock back into the tank. Very simple, very effective.

Listening to the program started me thinking about how I could possibly use his idea on a larger scale: be it for larger tanks or the raising of fry on a large basis. At the time I was raising lots of fry and was looking for a better, easier way. Some 15 years ago I had a “central system” that drove a 70 gal, a 55 gal and two 30 gal tanks. It had a 30 gal sump and an Ocean Clear canister filter. This system worked pretty well considering my limited knowledge at that time. Mike Jacobs and I then started talking about a central system for the fry and slowly but surely a system was developed. We were using 2 and 4 and 6-gallon plastic tanks to raise the fry and Mike had a “Marineland Tide Pool” filter that was to be used as the sump. He drilled holes in the plastic tanks to be used to house the fish, added bulkhead fittings to those fish tanks and set them on a fish stand so that they drained into a the PVC gutter which then drained into the “Marineland Tide Pool” sitting below. A pump then returned the water to the plastic fish tanks through a system of 1/2" pvc pipe. The return pipe was drilled and plastic adjustable air valves returned the water to each tank (above pic...pic 3).This system worked really well for us for 2 years. We had 14 of the plastic tanks running on it and we could have a couple of hundred fry in each tank and grow them up to ¼” on some species before we had to thin them out.

Now we needed a system for when the fry out grew the system we had. One very important factor to all of this, of course, was keeping the cost to set up this system to a minimum, but we need bigger tanks now. The cost had to be kept low without sacrificing functionality. This means the filter would also have to be bigger. I decided to use 10-gallon tanks, 17 of them (because 17 fit in the space). We had already rigged a ‘jig’ system for drilling tanks so putting in the overflow holes was not a problem. The tanks would be used the long way (you look at the end of the tank) so I drilled the tanks on the side, close to the top rim (pic 4). A bulkhead fitting goes in the hole and a short piece of PVC with an elbow will drain the water into a gutter(pic 5). A long piece of gutter with end caps on both ends will run the full length of the system just under the drains of the tanks (pic 6). Two holes are cut in the bottom of the gutter and 1-1/4” bulkhead fitting are placed in the holes. This is where the water will drain down to the filter (pic 7). For the sump I used a 40-gallon plastic tote (pic 8). For the filter I go back to what I was thinking about with the Henry Debruyn filter and using the lava rock as the main component. My idea was to have a container to hold the lava rock and it would have to have holes in it so the water can drip over the lava rock and then drain into the sump. Off I went to the hardware store looking for my container. I found one, it was 13” x 17” and 9” high, and all four sides were full of ½” square holes (pic 9). I lined all four sides with foam and I filled the container with lava rock and put another piece of foam on top. Because the sump is flexible I used some PVC to hold the filter box up off the bottom of the sump and to also help keep the sides of the sump from bowing out too much. To return the water to the tanks I used two Mag Drive pumps, one for each row of tanks. I used a 500 gph for the bottom row and a 700 gph for the top row. I used ¾” PVC from the pump and ran it over the tanks. I put in 2 plastic air valves over each tank and airline tubing running from the valves to the tank (pic 10).
I used these two systems for a year with success but it was time to make a few improvements. For the fry system I decided to increase the size of the system. To do this it will also need a bigger filter. I increased the system to 16 of the 6-gallon plastic tanks and I also added four 30-gallon tanks. There is also room to add another 8 of the 6-gallon tanks. For the filter I used the one from the second system and I will build a new one for it. On the second system I will be adding three 10-gallon tanks for a total of 20. I also have the room to add 11 more 10-gallon tanks to this system. Next I needed to make a new filter. Back to the hardware store to find a tote for the sump and a container for the filter. One thing I didn’t like about the other sump was how flexible it is so when I found a heavy duty tote that was not flexible I new that was the one (pic 11). Now for the filter box. I could not find the same type as the one I used with the other system but I found some milk crate type of boxes that will work and were a lot cheaper than the other one was (pic 12). I lined the sides of the crate with foam, filled it with lava rock and covered the top with foam. Since the sump was heavy duty I decided to set the filter box in the sump on top of a couple of bricks. The bricks held it 4” off the floor, which is a good height. I have been using the two systems in the latest configuration for about 1.5 years now and everything is working great. There is hardly any maintenance on the filter. I clean the foam piece on the top ever couple of months and change 60% of the water every 2 to 4 weeks.

The following is a parts list and approximate cost of the parts for the 10-gallon tank system. The costs are what I paid so your cost will be different:
20 10-gallon tanks - $60
20 ½” bulkhead fittings - $80
Glass for tank covers - $60
Plastic milk crate - $6
35-gallon heavy-duty tote - $16
2 bricks - $3
1 bag lava rock - $4
1” thick foam sheet - $15
12 2”x4”x8’ wood - $24
6 2”x4”x10’ wood - $28
½ sheet 5/8 plywood - $10
1 box 3” deck screws - $4
20 plastic air valves - $5
40’ airline tubing - $4
2 700gph Mag Drive pumps - $120
2 10” vinyl gutter - $20
2 gutter end cap pairs - $12
6 gutter hangers - $9
4 1-1/4” bulk head fittings - $26
Various PVC pipes and fittings - $36

The total for this system (pic 13) was $542. That is not a bad price for a complete system. There are companies that make these types of systems but a small one is $2000. I was able to get the 10-gallon tanks for $3 from our local club and with a little bit of work looking at different sources you can also build one for under $600.

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