Ok, I set up an ATO like you want on both of my tanks just last month. It works well, was a lot cheaper than the pump driven ones, and I only have to fill the reservoirs once a week. Would go longer, but I just fill them when I do water changes. Here are the components I used....

Amazon.com: Coolbreeze Beverages 2.5 Gallon Jugs with Pressure Sealed Lids, Water Jugs with Caps - Frozen Drink Mixing, Cold Brewing, Beverage Storage - 2 Pack : Grocery & Gourmet Food

Amazon.com: Coolbreeze Beverages 2.5 Gallon Jugs with Pressure Sealed Lids, Water Jugs with Caps - Frozen Drink Mixing, Cold Brewing, Beverage Storage - 2 Pack : Grocery & Gourmet Food

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Amazon.com : ZAOJIAO Auto-top-Off ATO Solution Auto Water Filler Adjustable Float Valve Mounting for Aquarium Sump : Pet Supplies

Amazon.com : ZAOJIAO Auto-top-Off ATO Solution Auto Water Filler Adjustable Float Valve Mounting for Aquarium Sump : Pet Supplies

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Malida 1/4 inch O.D. Length 32.8ft(10 meters) RO Water Tubing, Hose Pipe for RO Water purifiers System,+ 1/4 O.D quick connector 10pcs - - Amazon.com

Malida 1/4 inch O.D. Length 32.8ft(10 meters) RO Water Tubing, Hose Pipe for RO Water purifiers System,+ 1/4 O.D quick connector 10pcs - - Amazon.com

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Amazon.com: PureSec 1/4 Bulkhead Fitting 1/4 RO Tubing Use for RO/DI System(5, 1/4" Tube O.D.) : Industrial & Scientific

Buy PureSec 1/4 Bulkhead Fitting 1/4 RO Tubing Use for RO/DI System(5, 1/4" Tube O.D.): Push-to-Connect Fittings - Amazon.com ✓ FREE DELIVERY possible on eligible purchases

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I did have to add a rubber washer to the bulkheads, but I had some on hand.
Hope this helps and good luck!

 

Gravity fed ATO's certainly work. Even Red Sea uses/used them on some of their tanks. I am a one that enjoys some bells and whistles, and I don't have space above my tank or sump for an ATO reservoir, so I got this ATO. So far it works well, though the tank is still cycling. It is only a few $ more than the parts posted above and comes with everything except the reservoir. I use a 10g aquarium that sits beside my sump in the stand.

 

Awesome! Glad to hear it is working for you! Seems like a pretty similar component list. Im trying to avoid drilling into the glass top-off tank that came with my system. Thinking that I could install a tee and a valveat the highest point of the 1/4" hose and suck out the air to start a siphon. We shall see how it goes!

 

I tried to do a gravity fed ato but ran into the problem of not having my reservoir high enough. I ended up needing to buy an electric one. It worked ok even at a reduced height but needed to be re-primed every time I did a water change through the sump. My advice is to install a ball valve shutoff in the line to the sump so you can turn it off when doing water changes down there.

 

I had issues with the gravity fed one with the bottle from amazon. sometimes it would just flow out and over pour, could have been how brittle the bottle was maybe. Changed to an electric one and way better and a larger container so less to refill. $13 vs $50 for an electric reef breeders ato, wont go back.

 

Did you get the Prism ATO from reef breeders? Or the EXO? I was/still am considering one of their ATO's if the gravity option doesn't work out.

I got a small rolling cart to put reservoir on for my 75. It sits behind a drawer system that sits beside the tank. On my 40 I mounted a shelf on the side of the stand for the reservoir. Looks good. I don't mind imperfections if the wife says ok, cause I am keeping tanks, not running a public display....lol

Lol, We have 2.5 year old twins, and they get into just about everything. Keeping the top-off tank below the stand is a necessity! I do love the idea of a rolling cart! I will have to utilize that idea when/if I build a fish room!

 

I got a small rolling cart to put reservoir on for my 75. It sits behind a drawer system that sits beside the tank. On my 40 I mounted a shelf on the side of the stand for the reservoir. Looks good. I don't mind imperfections if the wife says ok, cause I am keeping tanks, not running a public display....lol

 

Lol, yea small kids can make a big difference in how things go. I guess I forgot to say that I use sumps on both my tanks so the ATO reservoir doesn't have to be so high above the sump. My bad, don't know why I didn't think to include that info in my original response.

 

No biggie. I am just curious who uses/used a gravity fed ATO and why you do/do not like it. Im more interested in how well the float switch worked with the gravity fed. 😀

 

My reef tank I have the tunze nano, and I was on eb@y one day and saw a new reefbreeders exo for $49.99 there are groups that post occasionally for that price. tunze has been solid, pump is loud, so far exo has been great on the freshwater tank i like its super quiet pump

 

I randomly saw this post and figured it would be about time to update everyone.
So far the "siphon" fed top-off works flawlessly. I made a plywood pedestal for the ATO tank so that I could maintain a siphon. The only bummer is that when I need to fill the reservoir, I have to use a pump to move water from bucket to ATO reservoir. Highly reccomend a system like this where applicable.

 

I use a small power head in 5gal bucket at floor level with DIY float valve for daily top offs.