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topoff - air powered vs ph?


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I've looked through a lot of threads about auto topoff systems (I've already ordered my float switch) but have been unable to find a clear advantage of using an air-driven topoff vs a powerhead. Is there a clear winner here? Here are some of the differences I can think of:





-doesn't hurt the pump to run dry

-can use battery-powered pump to reduce voltage through float switch



-pumps faster

-can use an open or imperfectly sealed container

-quieter? not sure about this, just my general experience with ph vs air pumps


-easy to add a bigger reservoir if I am going to be away for a week, then switch back to the less unsightly small container when I'm around

-I already own a small powerhead and bucket





-need a decent size, rigid airtight container. I have a 5g glass carboy but it is full of homebrew and not topoff water :)

-without a rigid container, pressure in the reservoir can continue to pump water for a short time after the switch turns off



-running dry will damage the pump

-requires a relay and power supply to reduce voltage through the float switch

-??always takes water from the bottom of the container, so it will give off a heavier mix if there is kalk in the water??


So which route should I take? I am leaning toward the powerhead approach but am open to all suggestions.


Thanks for your time,

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IMO, faster flow is a bad thing in a top off. You would rather add freshwater slowly to let it mix.


Like you, I had an extra pump lying around. So thats what I used.

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I have an air powered top off. The biggest drawback is the relatively small container. The extra flow when the pump turns off is not that much of a problem even on my 2.5. I had an extra air pump so that’s what I used. If I was to do it again and I didn't already have an air pump I would go with a power head. A way to get around burning out the motor is to add a second float switch to the top off tank. If the water level gets too low it won't allow the pump to turn on. The only requirement would be a float switch that could be fully submerged.

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I run a power head type and I don't use a relay never had a prob , I use the same float swich that californiareefs.com uses prety much the same set up but i built it my self. for the issue of your kalk settling get one more tiny ph and run it in the bucket to keep the mix stured up. oh yea I also have a ball valve inling to adjust the flow into the tank

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The only requirement would be a float switch that could be fully submerged.

forgot to mention this the float switch I mentioned in the last post can be changet to normaly open or normaly closed by turning the "bobber" upside down

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I have an air powered topoff. I like it a lot, but I've had a LOT of troubles getting everything the way I want it.


First, I used a polycarbonate water jug, which flexed too much and wouldn't seal right. Then I bought a 5gal glass carboy. Worked awesome, but the stopper was a PITA to get setup right and would leak after being removed from the carboy too many times. Finally, I ordered a different cap for the carboy (for a racking tube, with another plug covered opening for starting a siphon through the racking tube) and everything is excellent now.


For giggles, my topoff thread:


qfour20's air powered topoff


Incidentally, now that I'm using a battery powered airpump, the thing is almost totally silent. 5 gallons of topoff water will last me almost a week.


Good luck!



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  • 2 weeks later...

I have the same type DHoffroad uses sounds like. Nothing else needed but an extension cord and tubing if you already have a bucket and PH. BTW make sure you keep the supply to the main tank above the water line so nothing can back flow. ( Which ever way you go , make a snail gaurd out of a pill bottle.)

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I went with a float switch with a relay to lower the voltage though the switch. I use a minijet 404 turned all the way down and it trickles into my sump. Works quite well, takes about 30 seconds to replace about 1/4 gal or less. I like this method because you can use something like a regular 5 gallon bucket and it will work fine, no need for an airtight seal

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I built my own auto-topoff using a relay and float switch from Grainger, and a replacement windshield wiper fluid pump from an auto parts store. I power the pump with a small 9V ac/dc adapter from Radio Shack. If you get the right pump, it comes with its own mini-bulkhead type fitting, making it a snap to install in any plastic reservoir. I used a small square rubbermade type tote that held about 5 gal of kalkwasser. You can locate the wiper fluid pump above the bottom by an inch or so, so that it doesn't suck up the calcium hydroxide.


FWIW, I used this setup without the relay for several years with no problems- even if the pump ran dry for hours (maybe days!), but recent incarnations of this resulted in shorted out float switches if I didn't wire in the relay.

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I used a air powered ATO for my 2.5 gallon here at school, and have a PH powered one for my 15 at home. Here is how I have them set up and what I like:

Air Powered

Battery powered air pump, 32oz Nalgene(no flex so no problem with built up pressure), float switch. I made this whole system my self, pros are the small size and simplicity matches the scale of the rest of the set up. Con: bottle is too small go through it in two days(MH and closed hood), solution, ordred a 128oz Lab style Nalgene with thick sides will be settin up this evening.


Power Head

I bought the switch wired into the cord from Cameron at californiareefs.com its works great. I have it mounted in my sump. Reservoir is a kitchen trash can, i fill it with about 8 gallons of RO water, it lasts I think a week and a half, I dont really know I would have to ask my father as its his job to fill it up when I am at school. I have a maxi jet 1200 and 3/4 inch tubing for the fill line. Pro: keeps SG stable, can leave for extended periods, Con: voltage going through tank. Also it would be harder to get a large container air tight (thought you can buy large nalgenes) and if you wanted larger outflow line than 1/8 I think you would need a larger air pump. If you were to use the 1/8 tubing it would take forever for it to top up, I know slow is good but i mean how slow.



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Try this:


Get a windshield wiper pump from your local autoparts store - I have found that a 1993 Probe model is good for cost, ease of instillation and pumping power


Find an unused wall-wart around 9-12 VDC - now there is no problem with voltage and current through the float switch


Find a non-polycarbonate container - in case you want to mix Mrs. Wages Pickling Lime or Kasswaser. Polycarbonate will break in time.


now connect everything togther and Eureka - a low voltage, low cost autotop that does not need to be airtight.


And you get to keep your powerhead for premixing your saltwater for waterchanges..... everyone does this, right?

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Thanks all for your advice, after all this constructive input I have decided to go the powerhead route. I ended up using a pump for a fountain I built long ago (smallest Beckett pump) b/c it is only 60gph and you can turn it down from there. At first since it is only 10W or so I wired the float switch so the current was running through - big mistake. It stuck on and luckily I was checking every 5 min or so.


So I had to wire it up with a relay, got my parts from radio shack. I decided to make my own power supply (basic diagram at http://www.epanorama.net/circuits/psu_5v.html , you can leave out the voltage regulator and get away with a single capacitor, all it takes is minor skill with a soldering iron) but a 'wall wart' style would work just as well. I think I saved about $3 building it myself but it was fun and I think it looks nicer. I wired it up to a plastic box and put an outlet on it. For the floats I wired 2 float switches in series and clamped on a bit higher than the other as a backup.


Now it works like a charm, pumps slowly into my sump. Definitely nice not to require the airtight container, makes adding additional topoff water so much easier.


Thanks all for your input! I am sure my fish/corals appreciate the additional stability.

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Wall wart


A small DC power supply in which the AC / DC conversion electronics is contained in a box that plugs directly into a wall power outlet.


These are seen growing from walls all across the world. They come from phone answering machines, scanners, USB components, Zip drives, cell phone chargers.....

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