Gemini Circulation Powerhead

This is a very powerful powerhead made by Aquarium Products called the Gemini. It is a powerhead rated at 960 GPH and it sure does move a lot of water. The output of this powerhead can be felt 6 feet across the tank. The powerhead is not a submersible, the motor part needs to be above water. If you look closely you can see the water line marker across the lower clear part of the powerhead shaft. The powerhead is about 12 inches tall. I use two of these powerheads.

DIY Acrylic Brace

The Gemini powerhead comes with a brace for being mounted in the corner of an aquarium. However, I wanted to place mine on the side of the aquarium, not the corner of the aquarium so I had to make my own brace.

This shows the brace I made from 1/4 inch acrylic which is a little to thin for this. Thicker acrylic would have been better. I bent the acrylic over a gas stove fire and drilled out a hole where the factory supplied brace will sit and drilled three holes to mount the new brace to the inside of my hood.

Gemini Powerhead in Acrylic Brace

Finally this shows the powerhead inserted into the custom holder I made. The custom holder is held in place inside the hood with 3 wood screws. Since the acrylic I used was too this, I have the brace down low resting against the inside lip of the hood for additional support. I feel the weight of this powerhead would crack the acrylic without this additional support.

Acrylic Cutting Tool

This is the tool I use for drilling holes in acrylic. It is a specialized high speed rotary cutter called a spirAcut SCS. This tool cuts just about everything from ceramic tiles, wood, sheet rock, etc. I also used it for drilling bulkheads in my sump.

Bad Gemini Ball Bearing

Note: I've had this pump seize on me several times. Each time I was able to take the pump a part and oil the ball bearings. However, each time I do this the pump has gotten louder and louder. It is now so loud I no longer bother to run it. I went to a local ball-bearing shop (amazed my small town had a ball bearing shop) and picked up some replacements. They were about $4 each to replace, part# NSK 608Z.

Here you can see one of the two rusty ball bearings on the gemini pump. To get at this, you have to cut the sticker seal, remove the top black cap, and remove 4 very long screws that hold everything together. The unit can then be split into a upper half and a lower half. Remove the armature that has the ball bearings. Removing the ball bearings is no easy task but it can be done. Careful pulling with pilers and a few hammer taps on the steel rod.

Once the bearings were replaced I rebuilt the unit and tried it out. Still not as quiet as when I first got it, but it was much better. $8 in parts saved $80 on the purchase of a new unit.

Wood Brace to Hold Pump

The brace made out of acrylic always felt to flimsy to me. I had a fear of it breaking from the weight of the gemini and falling into my tank. I decided to remove that brace and build a new brace out of wood. It was much quicker and much, much, stronger.

The wood is roughly about 6x4x1 inches. I used a hole saw to drill a 2 ¼ inch hole which was a perfect fit. I then used my band saw to cut out one side making a U-shaped piece of wood. The gemini slides right in. The brace is held to the hood with four 2 inch wood screws. This made for a very, very strong platform.

Gemini in Tank

This is the lower part of the Gemini that is in the water. The output of the Gemini was so strong that I had some intense buildup of salt creep on the center glass, reflectors and bulbs. You can see in the picture where I used a small section of 3/4 inch flex tubing over the nozzle of the Gemini. I removed a U-shaped chunk of the flex tubing from the lower part which makes the tubing flatter and wider. This has completely solved my salt creep problem on the center glass and the bulbs have gone several weeks without needing to be cleaned.

Woke up to one of the Gemini's squealing like a pig. I thought another ball-bearing had rusted out. Got the replacements, lucky before taking the unit a part I tried it again. Doesn't squeal out of water, put it in water unit squeals. I figured out the rubber connection that holds the shaft is just a friction grip. The rubber has rotted a bit and no longer provides enough friction to grip the rod. The squealing sound was the metal spinning inside the rubber. I tried a two part epoxy and Marine Goop to glue the rubber to the steel rod. Neither worked. Finally I tried two very small plastic wire ties to squeeze the rubber and make the opening smaller. This worked great, solved the problem.