A rare situation

Automatic Topoff

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Newest information added at the bottom, last update 8 Dec 2008 at 10AM

The problem

One of the challenges of having a nano reef aquarium is keeping the water parameters balanced, and one of the biggest challenge to that is evaporation. As water evaporates out of the tank, it leaves behind dissolved minerals (salt) and the balance is thrown. My three gallon tank evaporates about a cup of water per day, which is enough to severely unbalance the tank if left unchecked.

I wanted a topoff solution that would satisfy the following goals:

  • Small footprint in the tank, since I don’t have much room to work with.
  • Runs for extended periods without human intervention, in case I am out of town.
  • Responds to water level instead of a constant drip that could easily overflow the tank.
  • Adds water gradually – a cup at a time in a tank as small as mine could shock the system.
  • Easily expandable to larger tanks as I upgrade over time.

Topoff Mk. 1: Gravity/pressure-driven

The first automatic topoff that I made for the tank was a sun tea jar situated on a shelf above the tank. The lid is sealed airtight, and a tube runs from out of the lid into the tank at the level at which the water should remain. The jar is filled with water and the pour hole in the lid is stoppered with a rubber plug.

The jar on a shelf about two feet above the tank.

Closeup on the jar lid.

Once the water falls below the level of the pressure tube, the seal created by the tank water is broken, and fresh water can flow from the spout of the tea jar into the tank until the level is raised enough to create a new seal.

The tube on the left is the pressure tube, it is slightly submerged in this photo. The tube on the right is connected to the spout on the tea jar and feeds in fresh water.

Pretty low tech and fairly crafty, but I could never keep it going for more than a couple of days. The water level tube kept getting clogged and the tank would not get filled up. Refilling the jar was also a pain in the rear; the shelf is well above head level and reaching up to pour cups of water into it is awkward. To top it off (har har), the capacity of the tea jar wasn’t as “set and forget” as I wanted it to be. It would work in principle when I upgrade to a bigger tank, but it would get drained in pretty short order as the volume of evaporated water increased.

Topoff Mk. 2: Pump-driven topoff

The new topoff is designed using electronic float switches, which open and close a switch based on water level. The switches would drive an Aqualifter, a small pump which moves about 3 GPH (gallons per hour) and can lift/push water about 60″ up.

A diagram of the new topoff setup

FS1, of course, is the switch that controls when the Aqualifter starts pumping. FS2 will make sure no pumping happens when the water level in the reservoir is too low. I also wanted a couple of lights on it (everyone likes lights): one to indicate when the pump is running, and one to indicate that the water level in the reservoir is too low so that I can refill it.

After consulting with a friend who has more circuitry experience than me (read: more than zero), we came up with the following diagram for the controller box:

Circuit layout for the topoff controller.

There isn’t a lot left to say at this point of the process, so here are some photos of the build.

The project box I’m using to house the bulk of the circuitry.

I like modularity, so the float switches will be connected using 1/8″ (headphone size) jacks. The jacks needed a 5/64″ hole drilled in the project box. I’m sure everyone cares about that.

A float switch, with a 1/8″ plug attached.

The project box with LEDs and jacks mounted and soldered.

The circuit board with all its components attached and wired into the box.

Somehow by not soldering since I was a teenager, I got better at it.

e: yes Russ, same circuit board as high school 🙂

The box was getting really crowded at this point, and the last thing I wanted was some stray wire crossovers between the AC and DC parts of the topoff, so I got a second, smaller project box and put the AC components in there. The two were connected by, surprise, a 1/8″ plug.

The AC components spliced into the Aqualifter’s power cord.

The whole setup.

Courtney designed the mountings for the electronics in the tank and the reservoir bucket. The most challenging part was to get the in-tank switch held high enough to keep the water at an acceptable level – just another part of the fun of a nano tank.

Cutting holes in the lid of a 2 gallon bucket.

The “reservoir empty” switch mounted on a piece of 1/2″ PVC, which was siliconed into the bucket lid so it dips down about seven or eight inches.

The finished reservoir bucket, with a plug for refilling and a water tube going to the Aqualifter.

The tank mount is a 1/2″ PVC elbow which was cut on one end to fit over the glass and notched on the other to hold the switch.

Proof that I could really use a drill press.

It fits!

Spraypainted black to fit in with the tank equipment. Also pictured: my new caulk.

Tank level switch is siliconed into place.

Everything in place on the tank stand.

Water level pre-turning on.

It’s pumping!

Drip drip drip. It’s very slow, which is good because the float switch won’t get shocked by waves and the tank won’t get shocked by cold freshwater.

Full tank shot. The PVC blends right in.

Courtney put this little piece of plastic mesh on the overflow to cut down on air bubbles, which were accumulating on the switch and pushing it closed.

It’s been running since about 8PM on December 7th, and so far everything’s great!

Future Work

As great as the Mk. 2 is compared to the Mk. 1, it can stand some improvements. The Mk. 2 was pretty much slapped together in the space of about two weeks because of the imminent arrival of Christmas and the corresponding departure of me. I did not want to have to leave the tank without a reliable topoff solution and come back to a dried out salt dune. I don’t have any plans to build a Mk. 3 right away, but here are some ideas that I’ve had for the next revision.

  • Use a transistor instead of a relay to drive the “reservoir empty” LED. The relay takes up a lot of room compared to a transistor and may be prone to mechanical failure over time. SomethingAwful goon babyeatingpsychopath provided me with this diagram:

    Transistor-based topoff diagram

  • Use a single wall outlet. The Mk. 2 uses two, one for the 12V transformer and one for the Aqualifter. It shouldn’t be too much of an effort to mount the contents of the transformer into the project box and have only a single cord going in.
  • Have two float switches in the overflow. The ideal setup has two float switches, the bottom one acting as the main switch and the top one acting as a safety in case the bottom gets stuck. This is less of a design flaw than a space consideration: I just don’t have that much room in a three gallon tank. The next tank I have will most likely be sumped, which will make the safety switch design much more feasible.

Written by Chris

November 26th, 2008 at 1:57 pm

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2 Responses to 'Automatic Topoff'

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  1. That circuit board looks suspiciously similar to something that had a bunch of traces vaporized off it in high school by some camera flash capacitors before we learned about “amperage” and “current carrying capacity.”



    5 Dec 08 at 2:24 pm

  2. […] Just to update my previous post, the new topoff is done and operating nicely. All the pictures are up on the project page. […]

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