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I used a propane torch to bend the test tube from a pH kit. It takes a little practice but the tubes are like $.50 so you can get a few extras. Teh trick is to spin it as you heat it and to make the bend, keep spinning it while pulling slightly apart and forming the bend.
 

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You're best bet for sealing that is to use heat and fuse the two parts together. Make sure the two peices are equal by careful trimming and/or sanding with the two halves jammed together. Then, heat a piece of metal on the stove or with a torch until you can just barely melt the plastic with it. I don't think there is any glue that wil stick to it for more than a few days.
 

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The weak part to this may be the hole for the suction cup. Hopefully though, the rubber will swell slightly when wet and prevent any leakage. The silicone may not stick very well but if it is only for small holes it will probably be OK. In hindsight, a way or heat crimping the joint may be best, similar to the way they seal those damn packages for portable electronics. Heated pliers may do the trick.....
 

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If I have done the math correctly, trust me, I probably did not....

Using NaH2CO3 to get 5degrees requires 75.18mg in 1 liter of RO/DI water.

For comparison, a penny weights 2.6 grams or 2600mg.

Anway, if you buy a 1 gallon jug of RO/DI (3.79liter/gallon) you need to add 284.9mg or .285g NaH2CO3. The only way to accurately measure this is to use a gram scale.
 

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Here is my contribution to the DIY drop checker:

Took me about 15 m inutes and a Benzomatic torch. Truth be told though, I have been dinking around with this for a few days and this is my 5th attempt. Not great but functional and fun to do. I never considered heating and actually blowing the end until hoppy suggested it. Also, you'll notice the end is broken, apparently a screw driver is not a substitute for a carbon rod to flare the end. After it broke I did heat the end so it is not sharp and the fishies are safe. This may turn out ok though as it broke at a real angle meaning that the water interface is a little larger than it would be otherwise. kH is 4.2 (Lamotte-80ppm) and solution has about 4 drops of indicator from the AP pH test kit.

 

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Ahh, good explination. The hardest part with mine was making the angle without it collapsing. I thought you were supposed to pull and bend but blowing and bending sounds like it would work better. unfortunately, all this is hard to do with a 3" long test tube. Blowing the ball end was really cool and I have never done anything like that before.

I may need to go find some glass tube locally...

Anyway, back to the subject at hand
 

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I just made one from a glass test tube. It doesn't look half as good as denis' though. I couldn't get the glass to bubble out at the end, just slightly rounded. Function over form I guess. Testing to see if it works now.
The trick for that seems to be hotter than you think and to put the tip of the flame directly on the corned of the tube where the 90 degree angle is.
 

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That's very clever. Well done. A suggestion though, next time try painting the inner tube white so that the color of the indicator is easier to see.
 

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Time to kick it up a notch!

OK, while I am discovering that I really like to melt glass (maybe a new hobby for me. I can be a double threat!) I just don't like the uncertaintly of this. The whole yellowish, greenish thing is just to much for me.

So, I give you the electronic drop checker:
 

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Re: the seal.

I started playing around with tubing and discovered thet my PinPoint probe was a good fit for 1/2" eheim tubing. Next, I played around and found a 5/8" forstner bit that was a good fit for the slightly expanded tubing around the probe. I pushed a short piece of tubing onto the probe, easiest when wet, and then forced (gently) the tubing/probe into the hole in top of the "checker". No leaks. I also know the tubing will expand a tiny amount when underwater for a while, which should improve the fit even more. YMMV with regards to probe size, tubing availibility and drill bit size. I probably got lucky that I had a bit that fit well.

An alternate method would be to use a specially made connector that holds the probe. I know IUnknown made an inline probe holder using one of these fittings.

Now, re: electrical interferrence, I have wondered about that several times in the past. Each time I double checked the reading with everything on verses everything off and unplugged. Never any issues.

Now, I have been using the regular drop checker for several days and find that with kH ~5 the indicator is yellow by the end of the day. The fish are fine, maybe a little skittish but fine. I have not adjusted the CO2 flow at all. My electronic drop checker (we need a name for this) has stabilized at 6.3 after 3.5 hours. The water to air interface is much larger on this than on the little drop checkers so I am pretty confident that everything is about right. The water in the electric version is probably not as alkaline as in the drop checker. My next step, now that it works, is to get some DI and make a proper solution of kH 5 and set the controller to ph 6.5, which will give me ~45ppm CO2.
 

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I finally got some distilled water and made up some kH 5 water. Here is what I found to be easiest: 6grams NaHCO3 raises 50 liter of water ~4 degrees. I can acurately measure 500ml so 4degrees in 500ml is .06gram. Now, my gram scale has a readout of .1gram so to get a nice round number, .06*5=.3g. So, add .3 gram to 50ml of water. That way, 10ml of that solution (suck it up with a syringe) in 490ml water is about 4 degrees. Test with Lamotte reads 4.04 degrees. So, add 2ml more and test again. kH=5 degrees.


I have a confusing issue now though. I mixed a small dropper bottle of this solution with 2drops per ml of indicator and filled my little drop checker. I also used the same 5kH mix w/o indicator to fill my electronic drop checker. I had calibrated the probe yesterday but the electronic checker settled overnight at a reading of 6.1. The color checker is blue green. There is definitely a big descripency but I can't think of what the problem may be. My initial thought is that the probe end, which absorbs water is effecting the readout.

Maybe I should soak my probe in distilled for a while to try and pull any kH in the probe out by osmosis. Also, I am wondering if I should use a lower kH in the electronic version since it may make the gas transfer happen faster- lower kH means biggger pH swings. I am thinking I should buffer to .5-1 degree for that.

Any thoughts?
 

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I'm not sure about that. A kH of 13 woudl mean you inject lots of CO2 before getting a pH change. That means you would OD you tank on CO2. I think better would be to use a very low kH so that the pH change happens fast and easily, allowing the controller to be more in control. I do not think it matters if the probe reading is at 7 or at 5, it will still be as accurate as the probes accuracy. What I mean is, I do not think that having a lower pH as the setpoint will compound any probe inaccuracies. Therefore, a lower kH will mean a faster response time... I think.
 

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I'm not so sure the breather bag idea works. I've had a couple differnt models in my tank for over an hour and there is no color change.
 

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I think Tom is getting that notion from the fact that he plans to use DO probe membranes. The DO probe has a fast response time and works basically exactly like he has described in his posts. As usual though, I don't follow his notion of cheap since I can't find any that are less than ~$25 per membrane. I obviously don't know where he is looking as he never tells....

The breather bags should work in theory though don't know exactly how they work. There might be an issue with pressure across the gradient, or lack of with water on both sides. I really don't know much about osmosis type functions, other than the basics of things wanting to be at equilibrium.

I'll let them float around longer. It is possible that there is to large an air space above the indicator sample. Let me say what I did... I took a small specimen jar with a snap on lid, about 10ml volume. I cut away most of the lid leaving only the outer rim. Placed a small piece of Kordon bag over the opening and snapped on the lid rim. Works great. The hole in the lid is about 1/2" diameter. I added 1ml to this and placed it inverted in the aquarium so that the indicator solution is sitting on the Kordon. I also made another that has a 3/16 hole but the container is 7ml and I used 2ml of solution. This one is tall and skinny compared to the first with is shorter and wider. Neither is showing a color change after ~3hrs.
 

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Might sound Crazy, but before you give up---how about flipping the membrane around and trying it that way?

Maybe they only let 02 in and C02 out--who knows? :rolleyes:

If it works after flipping--I would say the it won't maintain equilibrium, but would be like a one time reading.......Hope that makes sense.....:D
I tried that when there was no change after about 2 hours;)
 

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It does work but takes about 24 hours to get to equilibrim. It also never gets to the same color as my regular open end drop checker. The small holed unit never changes color and the one with 1/2" opening gets blue-green while the other, regular style is green/yellow.

The response time is actually so slow that it won't even stabalize over the photoperiod. :(

I still can't find a source for the Teflon Tom talks about. Ican find them listed but no prices or avialibility for seperate ordering. I wonder if by the time one goes through the 5 disks normally included with a DO probe that the probe needs to ba replaced as well. I see proces for the probes ~120. I don't know exactly what the membranes are made from, other than Teflon of which there are lots of types and thicknesses. I have seen the membranes listed as 1mm and .1mm but I assume they must be .1mm. I searched for .1mm Teflon sheet/film but there were lots of options of types, porosity, etc.
 

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Tom said the stuff is cheap. I don't think he would be messing with it as a realistic thing for the hobby if it were not. Obviously we are not looking into the same sources as he is. This Teflon stuff you finding now is pretty new but DO probes have been around for ages. We're just not looking in the right places.

Don't you just love how he always wants to help but will never really share the important stuff?
 

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Hoppy, your idea probably is not cheaper. I also hope they are not very permeable. I know gas molecules are pretty small but still....;)
 

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The well water could contain a lot of dissolved gases from ground sources, pressurizing and pumping. There may be other reasons for your results but it is certainly possible to have lots of dissolved gases present in a freshly drawn sample.
 
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