My DIY $50 nonelectric ATO -


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Having started my SW tank a short time ago. I decided, very quickly, that an auto top off was something I wanted.


I looked at many options - JBJ, Tunze, float switches, siphon systems, etc.
But I'm cheap, soI decided on a simple float valve system.
Luckily I built my own stand, so I have plenty of room.

My first objective was to find a container to hold plenty of RO water.

And I actually found it in the camping section at Walmart.

And luckily it came with a very, handy threaded cap.



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Next an adapter to fit in the threaded cap.

I bought it at Lowe's.

It's a 1/2 x 3/4 inch PVC bushing.
It screws right into the cap.
Be sure to use Teflon tape on the threads.

***cant get images to work with iPad. Will add images soon***
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The adapter is in the PVC section at Lowes.
Its sku number is 2552813558.
It's actually called SCH40 Bushing, threaded 3/4 x 1/2.
But the outside threads are 3/4 inch and the inside are 1/2 inch.
3/4 is needed for attaching to the cap.

Screw it into the cap after using Teflon tape on the threads.

Use a wrench and make sure to screw it all the way in.



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Next, is an adapter for attaching plastic tubing to the cap.

The float I found uses 3/8 inch tubing. So an adapter from 1/2 to 3/8 was needed. *from pipe to compression*

Here's the item.

Use Teflon tape and screw into adapter in the cap.

After that the cap should be ready for tubing.
The adapter is called a quick release, just insert the tubing and slide it all the way in. DONE. No tightening, no screwing, no Teflon tape. Just insert and it's water tight. 3/8ths tubing for this adapter.



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An on/off valve was need for refills.

The next item filled the niche.

This one works the same as the adapter. Just slide in the tubing.

I left about 12 inches of tubing on the cap which I attached to one side of the on/off valve. Then I attached the remaining tubing to the other side of the on/off. (Cut to fit after placing container near sump)

I bought 5 feet of it. (30 cents a foot or so) and had some left over.
It was just bulk 3/8's hard plastic. I had a Lowes employee cut it for me.
It looks like plastic ice maker line, but larger in diameter.



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Next I ran the tubing to the float valve.

The float valve has a compression fitting on the end.
Make sure to carefully remove that compression nut.
It has two 'washers' inside.
Carefully slide the nut with 'washers' over the tubing.
The two "washers" on the inside need to slide on just like they are.
Once they are slid on the tubing they are very difficult to back off.
It's best to slide them all the way down the tubing and off the other side if they need to be removed.
I wish I would have taken a picture of the position they should be on the tubing.

Once the float valve is connected to the tubing and cap. I would suggest disconnecting the components by using the quick release on the on/off valve.
Just push the tubing into the valve and then hold the plastic housing back.
The tubing should slide back out.

Float valve was purchased here:
I bought 2. One for back up.
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Gravity fed top-off systems are the way to go. I'm surprised more people don't go with them, but I guess it is a little difficult to incorporate adding a tank above your sump within a stand. I have a gravity fed system on my sump for my 9.2 gallon cube, and I just refill the 3 gallon jug weekly.

Simple, cheap, and not much can go wrong with a system like this.


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People don't use them because of their lack of redundancy, but I've had one running for years and have had no problems. Just need to clean salt accumulation from the hinge every now and then. Otherwise, couldn't be happier with mine.


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So the Aquatainer, float valve, on/off valve, and tubing were ready to go. But I needed some way to hold the float in place.

I have a 30 gallon aquarium as a sump.
And water levels can change during water changes. So I wanted a float that was adjustable.

I needed a flat piece of plastic and I found one at Lowes in the moulding section.
Some of the moulding that they sell is made of PVC. And that's what I purchased.
It was an 8 ft piece of flat, white, PVC moulding. No picture of the whole piece. But it is about 1/4 inch thick.

I cut it down to a 20 inch piece or so. And ended up with another peice about 6 inches. I used the two pieces along with some nylon nuts and bolts to build an adjustable bracket.

I used a table saw to cut a 3/8 inch slot in the middle of the 20 inch piece. I left several inches at the bottom with no slot for an area to attach the float valve to.

I drilled holes in the 6 inch piece for nylon bolts and attached the two.

I then drilled a hole in the bottom to attache the float valve, using the nut that came with it.

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To attach the bracket to my sump, I screwed a piece of the PVC trim to a piece of wood.
They are cut to fit snugly in my sump.
I then clamp it to the lip on my aquarium/sump.

Here is a video showing my test in a 5 gallon bucket:



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Finally the setup on my sump.

It works great so far.

The Aquatainer has 1/2 gallon incremental markings on the side so I can see exactly how much water is lost each day, and how much I have left.
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For those that might be interested:

The Aquatainer is about 12 inches wide on both sides and 16 inches tall.
So laying down it requires only 12 inches above the sump and a 12 inch deep stand.


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Parts list:

Aquatainer - 7 gallon - $12.50
tubing 3/8 - 5 ft - $ 1.50
3/4 x 1/2 pvc bushing - $ .50
1/2 pipe to 3/8th compression adapter - $ 3.50
3/8th compression valve - $ 8.50
Float Valve - $10.85
Flat PVC moulding - $ 5.00
Nylon nuts and bolts $ $2.00
Spring Clamps (2) - $ .70

Total $45.05

But I added a second Aquatainer for easy changes.
So I have about $60 in the whole setup.


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I run gravity fed for years ;utilizing a float valve used in furnace humidifiers ($7) a 3 gallon bucket which i recently changed out to a larger salt bucket. The only issue i have have is if i let the bucket run out, air gets into the 1/4 line and can take a while to be push through and allow water to flow. (most common problem i have with it) I run kalwasser from the bucket which require me to make sure line don't get clogged if to much kalwasser makes it into the bucket over time.
I also try to clean he float valve at least once or twice per year.
I can likely fix the air in line problem by having a T to allow air to vent out. ( still thinking on that as not sure if it will cause other issues).
So far for the last 5 years or so been happy with the system.