Mouthbrooder Egg Tumbler

This is an easy must do project for anyone breeding mouthbrooding cichlids. I don't have any pics, but next time I build one I'll be sure to snap some and get them posted.

What you need:
an air pump
a standard size gravel vac. Preferably with a removable top(where the hose attaches)
a sheet of fine mesh plastic canvas, I think I used #10. It just needs to have holes small enough that the eggs don't fall through.
a piece of 3/16" rigid tubing about 1" long will do. A barbed air line connector will also work.
an inline air line valve. A gang valve will also work if you are running other accessories with the pump.
a length of air tubing.
1 or 2 small suction cups
Small tube of aquarium safe silicone (i.e. GE I or other 100% silicone with no mold inhibitors) OR hot melt glue and glue gun.
Power drill with 3/16" bit and a bit that will work for the suction cups. It needs to be smaller than the nub on the outside of the suction cup, but not too small.
utility knife with fresh razor or hacksaw
sharpie or other marking device
scissors
ruler or tape measure

Measure about a 6" length of the gravel vac tube. Make a mark with the sharpie on the vac. I went all the way around to give a line to cut along. Cut along the line with the utility knife. Try to get a straight cut. For reference the end that you cut will be the TOP and the end that you leave alone will be the BOTTOM. Drill a hole in the side of the tube at about the middle for the rigid tubing. Drill the holes for the suction cup(s) on the opposite side of the vac as the hole for the tubing. The holes should be about 1/2 way between the middle and the end of the vac aka at the third points. If you are using only one suction cup make the hole 1/2 way between the middle and the top. Place the gravel vac with the top up and the bottom down on the plastic canvas. Trace around the tube with the sharpie. Using the scissors cut the canvas to the INSIDE of the mark. You should end up with a circle of canvas that will fit over then end of the vac without falling in or sticking out too much. If you don't have that try again. Cut a piece of the 3/16" rigid tubing about 1" long.

Now comes time for assembly. You can either use hot glue or silicone. Unless you are in a hurry and need it ASAP use silicone, it will last longer. Push the rigid tubing into the hole you drilled in the vac. Make it stick about 1/2 way into the vac. Put some adhesive around the tube where it intersects the vac. If it fits really tight you could get away with not adhering it. Run a generous bead of adhesive around the perimeter of the canvas circle and another small bead on the bottom edge of the vac. Having the vac sitting with the top facing down place the canvas over bottom. Add silicone as necessary to seal the canvas to the vac. Let it set for 24 hrs and put the suction cups on.

Now on to the cap. This is only necessary if you are going to use the tumbler in a tank that has other fish in it. It's main purpose is to prevent fish from eating the eggs. If you have a gravel vac with a removable top, remove it. Turn it so you are looking at the inside of the top/cap. If there is a flapper/check valve in the cap remove it so there the is just a hole. Now cut a piece of plastic canvas to fit over the hole. Neatness doesn't count here, it can be too big as long as it covers the hole. Adhere the canvas to the inside of the cap so it covers the hole. If you don't have a vac with a removable cap you will need to make something to go over the top unless you are going to have the tumbler in a tank with nothing that would eat the eggs. I didn't have to fabricate a cap, but here are some suggestions that may work. Try to find a piece of pvc or a union or something that will slip snugly over the vac. Adhere the canvas to the pvc as you did the vac. If you can't find something that will fit over the vac you may need to make one out of plastic canvas. You should be able to sew one together using fishing line. I have done that for breeder baskets before. It's not the easiest thing to do, but it can be done.

To use the tumbler hook up a length of air tubing to go from the pump to the tank. Attach the inline valve to the end of the tube. Now decide where you are going to put the tumbler inside the tank. Attach a length of air tubing to the tumbler at the rigid tubing and run it to the inline valve. Put the tumbler in the tank with the canvas side down. You're pretty much set, but you have to calibrate it I used sinking food pellets to simulate eggs, but you can go right to the eggs if you want. Put the eggs in the tumbler and if you are going to use a cap, put it on. Make sure that the valve is closed and plug in the pump. Slowly start to open the valve. What you are looking for is to have the eggs twitching on the canvas or gently rolling around, but not "jumping". A little bounce is ok, but you don't want them to come very far off the canvas.

The principal behind the tumbler is simple. Eggs sit on the canvas. As air is introduced into the chamber (the gravel vac tube) it has to rise since it is lighter than water. The movement of the air has to displace water, just as moving a spoon in a cup of coffee displaces the coffee. If the bottom of the chamber were solid the air moving upward would create a weak vacuum inside the chamber. If the chamber was made of a weak material and was unable resist the vacuum it would collapse. Since the bottom is vented, the air moving upward draws water up with it creating a vacuum that extends outside the chamber. The fresh water that is drawn into the chamber is theoretically more oxygenated than the water inside the chamber. That added to the fact that the eggs are rotating, even very slowly, provides the eggs with enough oxygen to survive. It is unnecessary and even harmful to have the bubbles pass over the eggs.

Just a side note; the air will be restricted at the cap and will build some pressure until it releases. The release will cause the eggs to bounce. This is normal, just try to limit it as much as possible. If you see any white/necrose eggs remove them. It is ok to treat the tank with methylene blue to prevent fungus growth, but I have found it to be completely unnecessary when using a tumbler.

Again sorry for the lack of pics, I will add them whenever I build another tumbler. Feel free to PM me for 1 on 1 advice.