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rabbit bottle topoff question


brandon429

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considering a larger rabbit water bottle to make a topoff for a friend and one for myself and wanted to ask someone who has used a bottle topoff about the mechanics.

 

-how much does the end need to be stepped down in tube diameter from the bottle output to function...does a smaller diameter contact tube stop the output of the bottle in some way? I wanted the topoff to be relatively slow and more accurate than a faster input.

 

-what are the dynamic changes with increasing the size of the container? most use hamster bottles, does the vacuum pressure relate to above volume in the delivery details

 

-can the setup be a little ways away from the tank, or does it have to be up close, within 6 inches? how far away can it run

 

thanks

 

remember the kent auto dosers that ran on drip with a pinch roller?

 

They had inconsistent rates from full to 1/4 full, less weight on the fluid through the roller...

if this is a reverse and the system only draws when needed by having a tube stick down at the max water line, then it should run sensitive when trained down.

 

Another major issue is direct contact with freshwater and saltwater. osmotic pull must slowly pull fw out of the bottle low to high tonicity so it also seems the system may be perpetually topping at some point in the design, but its based on restriction of the input tube Im pretty sure in guess

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As far as osmosis is concerned, a member did a series of tests for something like two weeks Nd there was no detectable salt in the fw. Can't find the thread right now

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thanks for the replies, I was thinking it would draw the freshwater into the salt...even so, that may be helpful

 

what the hamster bottle trick does is topoff your tank only when the level drops. you saw off the end of the metal tube so there is no ball, attach a rubber hose and put that end barely into the water line so that when it evaporates, the seal is broken and water drips into the tank.

 

when the water line is back up, the seal is reinstated and it awaits another drop, or feeds the topoff via osmosis Id have to bet money on it. you cant have freshwater not be pulled into a hypertonic solution, its a rule of biology just wondering if anyone has tried different diameter tubes to see what the right topoff rate would be

 

I know the hamster bottle idea works there's people in the pico forum using it, wanted to upscale 3x the size for long term use...

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thanks for the replies, I was thinking it would draw the freshwater into the salt...even so, that may be helpful

 

 

when the water line is back up, the seal is reinstated and it awaits another drop, or feeds the topoff via osmosis Id have to bet money on it. you cant have freshwater not be pulled into a hypertonic solution, its a rule of biology just wondering if anyone has tried different diameter tubes to see what the right topoff rate would be

 

Not sure if this will help but this is what I understand for the hamster bottle ATO's.

 

One possible reason the topoff isn't drawn into the salt is that saltwater is denser and the freshwater should 'float' as long as it isn't mixed. IIRC there have been articles about areas in the gulf that have "underwater lakes" where seawater with higher salinity forms stratified areas that look like lakes. Another good example would be the Baltic sea.

 

Still though, there is the question as to why the water wouldn't diffuse (as you said osmosis works by water being transported from a hypotonic solution to the hypertonic solution, however osmosis requires a semi-permeable membrane). I have two different ideas about this. The first is that as the seal is broken and the topoff begins to pour into the tank it creates an air pocket at the top of the bottle. Once the tank water rises above the water line it reseals the bottle (as you said in your post). Although the bottle is now 'sealed' there will be a portion of time that the freshwater is still leaking out of the bottle. This will cause the pocket at the top of the bottle to become large (however no new air is introduced) and thus decrease the air pressure. This will continue until the upward pressure from tank water (atmosphere pushes down on tank, tankwater pushes up on tube) matches the downward pressure from the topoff. This equilibrium state will not allow any more water from the topoff to flow into the tank.

 

The other idea has to do with some other posts I read about this same topic. There was the idea that the water and salt would mix and you would end up with a ATO full of diluted saltwater. For this case it is fairly easy to see this wont happen as the bottle is above the tank and there would be some form of energy needed to push the saltwater upwards into the bottle (saltwater is in tank -- lower potential; freshwater above tank -- higher potential). Or I guess you could simply think of how siphoning works.

 

Now moving on from that... larger bottle = more water = more pressure downwards. Larger diameter = higher flow. Not very helpful... I know :(

However, I am planning on getting a hamster bottle tomorrow to test out on my pico tank, so I'll try out some different diameter tubes and see what kind of flow rates I get.

 

Edit. Found the video for the underwater lake in the gulf

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From my limited understanding of this method, the reason it doesn't mix via osmosis is gravity. Saltwater being of a higher density stays in the tank. Sure, I imagine some of the spout may be diluted SW, not sure though. Also, it's been a long time since I was in school, however, I thought osmosis went from high to low. So a hypertonic solution would not "draw" on a hypotonic solution. Thereby between the hypo being elevated and gravity, it would keep the solution fresh. Again, it's been a long time since I learned any of this stuff.

 

The reason it doesn't all pour in is simply the vacuum created in the bottle. Once the spout is below the water line, no new air can get into the bottle. The bottle will still drain into the tank until the vacuum is strong enough to hold the remaining top off water until the seal is broken again. I imagine the higher you put the bottle and the thinner the diameter the hose would all aid in slower dosing. I don't think it would make a difference in the amount of FW dosed at any given time. Since the same volume of water removed is required to create a strong enough vacuum to stop the flow. The best you could do is slow the input of FW.

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Ray, you just put that in a much easier to understand way. Thanks!

 

Also, osmosis flows from lesser concentration solution to higher concentration. Something interesting to note though... diffusion says a gas will spread out from area of higher concentration to lower concentration areas (think perfume bottle opened in a room). This seems like it would be a direct contradiction from osmosis, however you have to remember that osmosis is based on diffusion through a semi-permeable membrane (only allows water to pass) so the pure water actually has the 'higher concentration' of water than the solution. It's just that we normally think of concentration in terms of the solute not the water... if that makes any sense.

 

Or if all else fails: Just think when you eat salt, you become thirsty. :)

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  • 3 weeks later...
CoralWhisperer

I made an ato with a 1gallon alhambra type jug.

I ran a 3/16 hose out the bottom for output, and a smaller "airline" hose out the top for air intake.

I siliconed the air intake hose to the side of my sump where I want the water level.

 

The only problem is that with the small airline tubing, the vacume is strong enough to suck water back up the air intake when the water level reaches it, effectively blocking anymore air from getting in the jug to release more topoff water.

So if the jug isnt more than 2/3 full, it wont function properly.

I am going to increase the air intake to 3/16 also and hope that will allow the air to get past the water.

 

 

Other than this small problem, it works really well and keeps the water level perfectly most of the time.

I even dose kalk in it, and the few glugs of water that come out each time it activates have not been a problem.

 

The 2 hose method should prevent any saltwater from getting vacuumed back up into the jug.

Like I said, just gotta get the right diameter tubing.

 

Maybe Ill get off my lazy a$$ and fix it today . . .

Ill get a pic of my ato when I start messing with it, so you can see what Im talkin about.

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I don't see the need for the air hose as you can just have the water come out from the other part and then it can't really have the vacuum effect. That's the point of the top off bottle. Something with one hose that controls itself and only opens when it isn't touching the water.

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