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Old 05-04-2006, 10:19 PM   #1
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automatic water changer description & questions

Hi all,

I have constructed a devilish mechanism to automatically filter/change the water in my new 20 gallon (little small but all I have room for right now) tank. Basically I am sick of having to deal with awful city water so I overengineered this device.

So now I have a reverse osmosis filter (consumer grade, from home depot) installed under my kitchen sink, and have tapped the output line and can run it to the fishtank where it trickles in by the filter. This way the fish and the people both get nice water, and the low output is fine since I have a small tank. I plan to cycle 5 gallons a day.

Incidentally the whole filter project has cost me less than $200.

Filter: $160 - $40 rebate
Tubes, fittings, etc.: $30
New high-powered heater: $20
R/O Right aquarium replenishment minerals: $16 for 500g
----
$186

Not so bad really and it will have the pleasant effect of cooling the tank somewhat in the summer, too.

The outtake from the tank works by the power of gravity, the tube makes a loop over the sink and at the tip of the loop, which equals the level of water I want in the tank, there is an airhole. As long as the tube never empties of water it will work fine. At least that is my plan.

Update: my plan totally worked!

Ok, two questions:

1. My incoming tap is hardness 120-140ish ppm. My output from the RO unit is hardness 50ppm. I was disappointed that it was still that high, I was hoping for more like 5ppm. Will this diminish over time? Is this normal? I am going to call GE but I thought maybe you guys could help too. Admittedly my dip-strip test kit is not precise.

2. Also, where should I position the intake/outtake within the tank? I was thinking I would put the intake by the filter I guess to encourage even distribution, and the outtake down under the gravel in the diagonally opposite corner. Maybe you have a better idea?

I realize that having the outtake low in the tank leaves a possibility of draining the tank entirely if the opposite end somehow gets ripped down, so I might not do that after all.


Anyway right now there is one zebra danio in there to help it cycle. We will see.

Everyone let me know what you think.

~perle

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Old 05-05-2006, 12:23 AM   #2
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I don't understand how your outtake works. You have a small hose with one end...

I just read your post 4 times, drew myself a picture, and now I finally understand. - Its simplicity is brilliant!!!!

An RO system should remove nearly all of the hardness. I would guess that your test kit is inaccurate. RO systems will get worse with time, not better (darnit). Verify your results somehow and if your RO unit is in fact giving off 50ppm, call the manufacturer.

The level of the intake hose is not importand. You may want to actually put it in the filter, if convenient. Close to the filter is also a good idea.

The level of input of the outtake hose could be very important if the outlet of the outtake gets lowered accidentally. I would suggest putting the inlet of the outtake hose above the heater and filter intake. This will prevent either of them being ruined if your water level drops.

Your outtake system will work the way you have it, but I worry that it may be prone to problems like getting clogged or bumped out of place. So be careful!

You have a very cool idea. Let us know how it turns out.

Are you planning to put in RO Right every day?
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Old 05-05-2006, 01:08 AM   #3
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For now I am planning to add R/O right every day. I will have to do some careful experiments and figure out how much is necessary (hopefully little).

Everything works awesomely, and I probably don't even really need that new heater which is in the mail (although it gets hella cold in the winter here in my poorly insulated apt, so it will be good to have).

Ideally I would add a baffle to the sink drain and run the filter and tank output pipes into that, underneath--I would rather not drip the tank water into the sink itself. But I have a rickety sink drain and it would be some work to rebuild it. I am trying to think of a more robust scheme that would avoid that.

You are right about the clogging, I am gonna leave the outtake tube about 3 inches from the top of the tank. That limits spillage and would save my fish in the event of an accident that drained the tank too quickly. I think I should maybe get an overflow monitor. Since this has no electric parts (not even in the filter system) I have no way to make an automated shut off, though. I have seen other people do complicated things with microchips and pumps and I am glad I avoided all that. Water pressure is all you need, really....

Note that after the exit tube loops out of the tank, it should at no other point rise above the level of the desired waterline. Also, you have to prime the tube by sucking on it.

Question: how, uh, "diffusory" is the circulation in a tank like mine? I have a Penguin 150 splashing into it. Do I need to worry about dead spots that would miss getting the new water, or having wide variations of chemical concentrations that would harm the fish?

Ok, here are some more pictures, below.

~perle
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File Type: jpg fish2_002__wince__211.jpg (11.9 KB, 468 views)
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Old 05-05-2006, 01:17 AM   #4
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i'm still confused, make a diagrma on paintbrush lol
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Old 05-05-2006, 02:11 AM   #5
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I would worry more about "cold water" spots building up, than "soft water" spots. This really should not be a large concern - especially the way you have the inlet next to your filter.

If I understand, Perle's outtake system is just like the siphon on a gravel vac. Stick one end in the aquarium and point the outlet of the vac towards the ceiling. Water will come out of your gravel vac until the water height in the aquarium is the same height as the outlet to the gravel vac.

Water will stay in the "U" shaped portion of the hose, keeping the "siphon." Then when you raise the water level in the tank, water will siphon out.

If I am seeing the pic correctly, after the end of the siphon hose, there is another hose to take the water down to the drain.

Perle, can you control how fast RO water goes into the tank? RO systems typically are 30 to 100 gal per day. I would think you would want more like 5 gal per day.
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Old 05-05-2006, 02:04 PM   #6
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Ok, yeah I figured the input rate is so low and the turbulence of the tank is high enough that the temperature would stay even throughout--even though it could be significantly lower than room temperature. A high-powered heater should take care of that.

I have a little valve/knob on the input (both ends actually, one under the sink, too). This lets me limit the pressure in the tube at the sink end, and shut it on and off or make finer adjusts right at the tank. Incidentally those valves are only like $3 at Home Depot.

You are right about the U shape. I have discovered a small issue with the outtake. The point of the airhole in the exit end of the tube is to collapse the suction of the hose at that point. However it is not a big enough air gap for the fill rate I think I would like; surface tension in the water limits how much air it can take in, so the outtake is slow.

I have some plans for solutions to this but I haven't decided which is best yet.

Anyway the ability to change the water in your tank simply by turning a knob continues to amaze me.
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Old 05-05-2006, 02:48 PM   #7
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pretty cool - one thing I wondered about rodi water - does the system dechlorinate it for you?
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Old 05-05-2006, 02:54 PM   #8
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The activated carbon prefilter completely dechlorinates it. I empirically tested this fact with a dip stick.

Incoming tap reads at about 1.6 ppm chlorine, no chloramine, which matches the city's published results. Post-filter water has 0 ppm chlorine, no chloramine.

~perle
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Old 05-05-2006, 02:57 PM   #9
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Quote:
Originally Posted by perle
The activated carbon prefilter completely dechlorinates it. I empirically tested this fact with a dip stick.

Incoming tap reads at about 1.6 ppm chlorine, no chloramine, which matches the city's published results. Post-filter water has 0 ppm chlorine, no chloramine.

~perle
very cool
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Old 05-05-2006, 03:34 PM   #10
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I don't expect that the size of the air hole would be a problem. Air flows much easier than water, and the air flow should be minimal anyway. Air does not need to flow through the air hole because it just a pressure relief.

A few hints (which you probably already know) to increasing the outtake flow :
- Lower the height of the suction break / airhole
- Increase the size of the outtake tube

Did the tank overfill when you turned on the water? It is normal for the water to rise as it builds enough height difference to drive the siphon.
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