Neptune Aquatics

How many gallons for automatic water changes?

alve

alve

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I had been thinking about setting up a system for automatic water changes for quit a while now. I purchased the Litermeter III pump with water change module and set it up today.
Just calibrated the pumps and was wondering how much water to change daily. For now I have it set up for 3.5g/day and since my setup is about 200g it would come down to 50% (105g) being replace monthly. Would this be enough or should I bump it up?
Since constantly only small amounts of water are being replaced I can imagine that it doesn't have the same effect as doing for example a 25% water change bi-weekly?
 
That is correct. Small changes are not the same as a large one, even if they add up to the same. This is because the second change is only effecting the "residual" of the first.

50% water change = 50% water change
sequential 25% water changes = 44%


1-(1-.25)^2

1-(1-%change)^# of changes

so, if you do 30 sequential 3.5 gallon water changes on a 200gallon tank, you are effectively doing
1-(1-(3.5/200))^30
=41% water change equivalent
A lot of people do 10% weekly water changes, so your # works out in a good range. Your's however would result in a more stable system since the "spike" change is spread out.


hth
 
Thanks for the info Tony! I could imagine that small amounts at a time wouldn't exual a big water change at once but now I actually understand it with your calculations. I might bump it up a little bit so I get to 45-50% monthly.
 
Thanks for the input Mike and Tony!

Jay, it's very easy. The Litermeter III pump removes a set amount of water every day. That amount is spread over 150 times a day that the pump kicks on so those are very small amounts each time. At first I was worried that my auto top off would kick on whenever it removes water but the amount is so small each time that it doesn't affect the auto top off.
The water change module is another pump that also kicks on 150 times a day and puts back the same set amount of NSW.
Once all lines are installed you can calibrate the pumps so they both move the same amount of water.
 
Interesting. How much would a setup like this cost and how much space would it take up? Combine this with an autofeeder and you've almost got a maintenance-free system!
 
I'm so lazy these days, I need to get an auto water changer.

What's needed? Litermeter III, a big resevoir of premixed saltwater, and some kind of controller? I have an aquacontroller III already, which also only turns on my auto topoff a twice a day (so that wouldn't kick in during the water changes?).
 
Ok, scenario:

I have 2 of those APT peristaltic pumps.
Am I correct assuming they both pump at the same rate or pretty close to it? (isn't that the whole nature behind peristaltic pumps?)
Could I just hook 2 of these up on its own power source, have 1 fill and one drain a few hours a day controlled by a RK2 or something?
Does head pressure affect peristaltic pumps? (Worried about it draining faster than it fills)
 
Yes head pressure does affect perstaltic pumps. So it will not pump at the same rate unless the head pressure is the same.
 
In that case, I wonder how close I could get it using one of those variable voltage plugs from radio shack.

Besides that, anything else to consider before I go and try it out?
 
If you want to get really creative you could have your pumps hooked to timers inline with float switches, have your pump that pulls water out go into a bucket (whatever) with a float switch and the timer basically once a day pump until it triggers the float (you pumped enough), then an intank float switch and after the stuff pumped out it pumps in until it triggers, have the timers only on for a set period each day so you don't accidentally top off what should be freshwater (which is on another switch which triggers before any water changes take place ;)).

Ok maybe that's a tad complicated, and you still have to empty the bucket each day :D
 
Kinetic, you need a Litermeter III (pumps water out), a waterchange module (pretty much a second pump that pumps NSW in) and a reservoir for NSW. No controller is needed, the Litermeter III takes care of that. You don't need to turn off your auto top off because of the very small amounts that get exchanged at one time.

Jay, for calibrating the Litermeter setup I had to run all tubing first. Ones all is installed I had to calibrate one pump at a time with turning on the pump and letting it run until it fills a measuring cup exactly to the 500ml mark. Then the same with the other pump.
The litermeter calculates for each pump what the amount of flow/min is. One of my pumps has a higher flow then the other one because the length of tubing is much shorter so that one will pump less long then the other one each time they run a cycle.

You could probably do a setup and measure for each of your pumps how long it takes to fill 500ml and after wards calculate how long to turn each pump on with your controler so they move the same amount of water.
 
just curious, how do you do it. Do you pump 3gal out first, then pump 3g of new water in? Would you let it runs while you're on vacation?
 
I currently use the LM3 auto-water changing setup on my tank. (Check my tank thread for some photos and a diagram)

Head pressure definitely affects the peristaltic pumps. When I used the pumps on my tank in the kitchen, I was pulling water from 70 feet away through 1/4" tubing and the rate was something like 1/5th of the flow rate with the container and tank in the same room.
 
My length of tubing would be at most 3 feet vertically, I could move a couple things around and make that about a foot. I can't imagine 2-3 feet of water in an airline tube (3/8"??) weighs all that much to affect head pressure that much. I guess I could get 3 feet of airline tube, fill it with water, measure it in ml, figure out how much it weighs. When I get some time I am going to play with it.

Either way, I could run the pump that pumps up into the tank at 12v and the pump that pulls out water at 9 or 7.5v I think. I'm pretty sure these pumps wont move at any under 7.5v
 
This looks like a really good investment. However there's one thing I can't grasp; for the NSW reservoir, how do you account for evaporation so that continually concentrating saltwater does not enter the aquarium?
 
Hey Tony, could you do some of that fancy math for me?

Assuming the pumps I have will do at a maximum 5.6ml an hour; I would run the pumps 3 hours a day which would change about 1008ml. 1008ml x 7056ml. 1.86 gallons in a tank with about 25 gallons of water in it. That's only like 7.5% water change every week without the dilution factored in right?
 
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