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Nanocube auto-topoff design ideas/concerns


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Recently set up a new nanocube and I have to add about a half gallon every day to the tank as I have both fans wired to run constantly to keep the temp down. Makes it hard to go on weekend trips and such. Here is my idea for an auto-topoff system based for a JBJ nanocube. There is like NO space to work with so this is the best I could think up. I keep my water level pretty high, about a few mm's below the sump divider.





I'd like to drill a hole in the direct rear of the hood, and pass a 1/2 inch pvc pipe with 90 degree bend through. Wire the float valve to hang from that down into the sump water. Wire up the float vavle as others have done to a powerhead in a reservoir. My concern is that when I tilt the hood back, the float valve will fall and the pump will turn on. My way around this is to wire a switch inline on the float valve, and arrange it so the valve only works when the switch is on. Any suggestions or concerns which I might have missed?


I'm not even sure if there is enough room back there yet to make this all happen. I want the tank to stay as close to the stock look as possible so drilling down from the top is out of the question. What do you guys think or those with nanocubes and auto-topoff systems, please post how you did it.

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This looks like a great Idea, I have the exact same problem. I have been doing a lot of research on this but I am still confused about the whole set Up, I would Like to follow your thread to see how your Idea turns out and hopefully some more people will join in and help find a solution for this.


I think your basic set up is a good one but like you said the only problem is with the hood lifting up and causing the float valve to start the pump. the switch solution is a good one but how much more wiring will be involved?


If anyone has already done an auto-top of system for their nano cube, any information on how you did it would be great.

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dont think the switch will require much more wiring, probably just two more connections/solders. I'm more concerned with the amount of space, or the lack thereof. ;)

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Almost the exact same setup as I have on my 2.5 gal. The only difference is mine is an air powered top off. I have an air tight container with one tube in from the air pump and one out to the tank. When the pump turns on air enters the container forcing it into my tank. It works great. If you are short on room why use 1/2" pvc? Regular 1/8" ridged air hose would work fine. You would just have to put a bypass on the pump so you don't burn out the motor.


All you need to do is cut one of the wires in an extension cord and solder in a float switch. I am working on adding a relay and a transformer into the design. I never liked the idea of having a switch carrying 120 volts in my tank. But it has been there for almost a year and I haven’t had any problems yet.

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The relay would act as a switch. A lower voltage (~6) would be used to activate the relay to switch the higher (120) voltage on. That way you wouldn't have the float switch carrying the full 120 volts it would only be carrying enough to activate the relay. The float switches are rated for 120 volts but I am always nervous about having it in my tank at that voltage. The transformer would be step down then 120 ac to 6 dc.

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I believe that most float switches are low voltage (12 volt) and not designed to handle 110. There was a thread about this catching fire.


Here is a top off system I made for my nanocube and is attached to a 5 gallon jug. So I only have to change it about every 2 months.



Dual PIK relay (radioshack)

12V power supply

Snail guard - 35mm film container with a bunch of small holes drilled in it

I made the adjustable holder out extra powerhead accessories.


You can make a float switch holder out of plexiglass, just cut and glue some small pieces together to make a clip that will attach to the back of the tank. Also cut out a 3" x 3" square out of the top of the canopy so when you open it the float switch is not affected.

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Hate to say this now, but do you have a diode like a 1n4003 or 1n4004 mounted across your relay contacts to supress the surge when the relay shuts off. It is a really good safety feature. You have to look up orientation though. I think it is cathode to the +

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I am by no means an electrician so I ran my set up by an experienced electrical guy before I hooked everything. The relay is designed for 12V on one side and 110 on the other. Its been has been working perfectly for a few months now.

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great setup, im gonna attempt to follow in your footsteps, but wow 5 gallons for two months? I'd go through that in 10 days. I wired my hood to have both fans on 24/7 which makes me have a lot of evaporation :|

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The relay I used had 6 legs and a push on base (so the relay can easily be replaced if it goes bad). Different relays may vary so if its not labeled (they never are) you would need to get a 12v DC power supply and a test light to figure out which wire goes where.


Sorry I couldn't be more help I don't recall the exact wiring for the relay.

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You can get a dual pik (120V part of the relay) and wire it so both would have to be closed for the powerhead to get power. Its like having two relays. So if the relay was to fail odds are it would not flood the tank and just stop working.

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Hi all,


Let me get this streight, both wires on the 120VAC electric cord pass through the relay, are acativated by the 12VDC volt side and activate the pump. Having both 120VAC lines go through the relay, this is what helps prevent overflow, or is it both 12VDC going through a relay?


I'm looking to build this as well for my 2.5G betta tank for testing before I start my 10G nano reef.


Does anybody have the radio shack part # for the relays they have had success with?


Thank You.


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