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Auto Top off opinions


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I am think about getting a auto top off system going, as during these wonderful winter months I am getting a fair amount of evaporation especially now that I have removed the glass lid.


I am thinking about using an ultralife float switch, and a 3-5 gallon jug with RO water under the tank, or I am open to suggestions. I don't want to do a gravity feed system if at all possible.

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Two popular choices are the JBJ ATO and the Tunze Osmolator. All three choices (including the ultralife) are listed here with a few specs:



Im using the tunze ato. Its actually a laser sensitve ato. I bought it for the peice of mind that its potentially safer to use than a laser switch, rather than a float switch. Its also super precise (great for nano's!).


Happy reefin'

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  • 2 weeks later...

Are you a DIY-er? I set up my ATO for less than $10 and I couldn't be happier with it. Get a float switch from floatswitches.net and hook it up to a small pump inside your reservoir, and then have tubing go into the tank.

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You need to be careful just hooking up float switches up to a pump (make sure it can handle the current of the pump). It is usually a good idea to connect the float switch to a relay that switches the pump on and off.


I would also highly recommend having dual float switches, one that switches the pump on, and another slightly higher that will switch it off should the lower one get stuck. I had a single float switch on my nano and it pumped an entire bucket of freshwater into it twice because the switch gets stuck (even with a snail guard).


I have seen the ultralife switches and all they are is a float switch, relay, and an outlet. I wouldn't recommend one of these because all they have to connect the float switch to the tank is a REALLY crappy suction cup and no guard for the float switch. If you aren't up to DIY I would recommend autotopoff.com.

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an auto top off system is simply something you setup to automatically add fresh water to your tank to replace water that has evaporated.


Most use a float switch. A float switch uses a little foam bobber that floats at the surface of the water. When the bobber drops, it turns on an outlet and when it rises, it turns the outlet off. You can then hook up a water pump or solenoid valve to that outlet to add water to the tank.


There are other kinds, but I will let you search and read up on those yourself

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Go with the litermeter III, it is a bit pricey but you get what you pay for, you can use a float swicth with it, But i just figure the average amount of evaporation and set the pump to it, maybe once a month or so i might adjust up or down, and of course for seasonal changes. It has a nonvolatile memory ( means that loss of power does not mean loss of settings or programs) so you can use it with a timer if you want. been running it for 5 years now and the the only maint i do is recalibrate it when i get board. I run it thru a kalk reactor that feeds two tanks. I can leave it unattended for up to 8 days before i need to refill the source water tank. Great for weekend get-aways.

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the best is daily addtions, but if weekly additions fit your schedule and your tank looks good then go with that. I like the Litermeter thing just because if i decide to just Juant someplace for a week or two i know the system will be taken care of. what you might want to do is mark the water line on your tank and each day if it drops below that line just add some RO/DI water back to that mark, and every so often check the salinity from time to time.

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It looks like it will work, but there are no real details as to what it is, and i really dont trust to much of anything on ebay. I dont believe in paying for information. Try searching the DIY forums here and on reef central and you will most likely find the same or similar instructuons for free not to mention you will be able to have a two way exchange with the builder if you have any questions or problems.

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I took a peice of tupper ware and poked a really tiny hole in it and put water in on top of the acrylic so it falls into the water drop by drop


its free

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i have an ultralife float switch in tank... i made a snail/wave guard using a kodak film tube... so far no probs B)

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To answer your specific question, I am using the JBJ auto top off and, w/ one small exception, it works great. The exception is the float switch. It's attached to the tank w/ a suction cup, and will fail after a period of time. I have, based on a reco from a forum, super glued the cup to the tank and all is working fine.


I have the switch controlling an air pump that I already had. I have adapted a 64 oz plastic juice container to act as the reservoir. There is an air line feeding into the lid and a water line feeding from the reservoir back to the tank. The switch turns the air pump on, which creates pressure in the reservoir, which forces water into the tank, which turns the switch off. I go through 64 ozs of RO water per day, give or take.

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