Aquarium Top-Off Tank

Aquarium Top-Off Tank

Top Off Tanks
PIC 1: Top-off tank made from 4″ PVC and coupled with 2″ PVC pipe.
Top-Off Tank Construction
PIC 2: Top-Off Tank Construction – Note: Reducer glued on as a built in funnel
Top-Off Tank Bottom Sensor
PIC 4: Top-Off Tank Bottom Sensor – Note: I had to file the rounded pipe flat to mount the sensor
Top-Off Tank Sensor Top Section
PIC 5: Top-Off Tank Sensor Top Section
Top-Off Tank Sensor Top Section Looking In From Bottom
PIC 6: Top-Off Tank Sensor Top Section Looking In From Bottom – Note air tubing for aerating the water so it does not become stale.

After seeing the web site of a guy who built an aquarium that was controlled by an Arduino controller, I noticed he had an auto top-off tank to keep his tank full is the level drops.

So I thought I would add an auto top-off tank to my aquarium project as well. I noticed from his site that he had built a reinforced 5 gallon wastebasket into his custom tank stand. However; I am using my existing prefab stand, and it doesn’t have any room for such niceties.

I really wanted a top off tank on my setup and so had to figure out how to do this. One thought was to build something like a box that would sit next to the tank, but picturing that in my mind I thought it would look really stupid. I really wanted something that would not show from the front (mostly), or at the least, not very much.

After considerable thought, I finally decided to create 3 tanks (pic 1) made from four inch PVC and strap them to the back of the stand. I built and coupled them with two inch PVC to try to keep my water volume up as high as possible without being ridicules. I knew I needed to allow air to exit and enter each tank as the water fills or leaves and so I decided to add a pipe and a drain valve to the top of two of the tanks. On the other tank, I glued a four inch to two inch reducer on top on another one to create a funnel to aid in the filling of the tank. (pic 2) I also made sure this tank was on the right side of the aquarium so it would be easier to fill since the TV will be on the left.

Right Angle Float Switch
PIC 3: Right Angle Float Switch

I felt I needed at least three float sensors for the tank and decided to put them in the middle tank. I made the middle tank so it unscrews in the middle to allow access to the float sensors. I decided to use right angle float sensors (pic 3) throughout the whole top-off tank. Ebay handled this easily. After allowing time for them to arrive, I began my work.

» First, I installed a float sensor at the very bottom in the “tee” section of the connecting pipe in the center tank. This will be the “Low Level Warning” or “OUT” sensor.  I had to file away some plastic to create a flat spot in order to mount the sensor. (pic 3)

» Next I installed one in the top of the top section of the tank to indicate “Full.” (pic 5)
There will be an LED mounted close to the funnel tank so when the tanks are full it illuminates to give me an indication to quit pouring in water when filling.

» I then installed one further down to give an indication of needing to refill the tank when water reaches this level. (pic 6)

I also added air tubing to all three tanks and even the connection tubes to allow the top-off water to aerate so it keeps fresh. The Ardiuno controller will kick this aeration off about 2am for an hour or so every other day, and I assigned my older and wee bit nosier air pump to fill the task.

Click here for more info about the top-off tank aeration


A quick note about the top-off water in a saltwater aquarium. When the water in a saltwater tank evaporates, it leaves and the salt stays.  So when adding water back into the tank due to evaporation, you want to refill it with fresh, aerated aged water. Topping off with saltwater would cause your salinity to rise to unacceptable levels and poison the tank.


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