Mod the PH pen? - The Planted Tank Forum
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post #1 of 28 (permalink) Old 02-27-2017, 04:22 PM Thread Starter
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Mod the PH pen?

I've noted in several posts that I was interested in knowing what the CO2 content of my tanks might be at different points in the tank. Do I have good circulation at all points or are there places which get less flow and less CO2? Not something a drop checker can tell me, so I went for a PH pen, not wanting to go full bore with a stand alone PH monitor. So the question became one of how to make a pen read down 15-18 "deep in the tank. You can't stick the electronics underwater, can you? So this is a simple DIY solution to sealing the works.

I found the pens to be really cheap and easy to find on the auction so got a couple on hand. By a lucky stroke, I chose one that comes in a plastic storage case which makes a really easy way to water proof the electronics when I want to fully submerge them.
Plastic box with the pen inside, sealed against the really low water pressure in our tanks, mounted on a flat strip of wood with wires going up to a micro switch.


I cut an opening at the bottom for the probe sensor to stick out and then sealed it and the rest of the box.
When mounting the box, I left some wood extending below the probe sensor to keep me from getting careless and sticking the probe down into the substrate!



The plastic box is not totally clear so it does make the readout a bit fuzzy but still useable.



With the stick cut to the fit my deepest tanks, I cut a momentary contact micro switch inline with the normal switch, leave the first switch "ON" and use the micro when I have it in position for a quick reading.


With the pens using three button cell batteries for a total of 4.5 VDC, I see no need to insulate the contacts, etc. very much. One other idea, I considered but rejected for now was using a wall-wart 5VDC power supply to replace the batteries. Not hard to do but for now, I will see how long the batteries last, rather than fiddle with the cord and plugging it in.
It seems to work as planned but there are still some things to question. One is how long the probes will last as they are shipped with nothing to keep the sensor from drying and that is one of the main faults with PH sensors. If they are not stored correctly, they fail sooner than necessary.
Given time, I think I will be able to judge my CO2 content much better than just using a single point in the tank as drop checkers might give us.
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post #2 of 28 (permalink) Old 02-27-2017, 04:40 PM
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i love it, look forward to what you find out. hear a lot about flow and CO2 distribution... would be interested to see how much weight this really has
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post #3 of 28 (permalink) Old 02-27-2017, 08:24 PM Thread Starter
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How much of what I read is really correct? Does the CO2 stay or does it float to the nearest point and just go straight up?
I will take a few readings each day, once I feel the sealer is safe, and see if I can tell more what's up. I currently have three tanks with pressure CO2. All have reactors of the Grigg's style but two are different size than the third but all of them have different layouts for the incoming water, different number and type of plants as well as far different flow from filters.
What really pushed me over into doing this was the amazing change I got when I changed the intake on my 125 gallon.
For a time, I seemed to lose touch with what it took to get the easy plants I use to do much growing.
Things like sword and red tiger lotus which had tried to stuff the tank full were just pretty slow even though I "thought" it was all near the same.
I keep a log of anything that seems it might come back as a question so I did some reading and found the only thing different seemed to be the spraybar I removed from a stock 2217 input. It seemed like a small change and there seemed to be enough circulation with the 2217 and a 2075 for filters and a Koralia nano powerhead to push water around the tank.
I got an amazing bump in growth when I added an el where I had removed the spray bar and then ran a tube down the back wall so that the CO2 rich water comes out aimed down and around the tank. Due to plant mass and rock piles, this tank would be difficult to meter and make sense but I do have a 20 and 75 that should make it easier to get the right read on the results.
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post #4 of 28 (permalink) Old 02-27-2017, 09:22 PM
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As far as probe life, I have had one I bought on Amazon about two years ago that looks just like yours. I had not used it for about two months. I got it out two weeks ago and set it in the calibration solution and found that it was only off by .02.

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post #5 of 28 (permalink) Old 02-28-2017, 01:45 AM Thread Starter
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As far as probe life, I have had one I bought on Amazon about two years ago that looks just like yours. I had not used it for about two months. I got it out two weeks ago and set it in the calibration solution and found that it was only off by .02.

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That's a good note to hear. Assuming it will last at least a year, I can get that much value out of it. I never know how to feel about stuff for a year or so. Thanks for the info.
I've not got too many readings yet. Seems once I stuck the meter down further in the tank, I found another hole that I had completely missed sealing!

At least the leak is not one where it let enough in to hurt anything and I can just let it settle around the bottom so that it doesn't require a whole new sealing.
But it does put off doing more of the deep readings that I planned.
Patience is something to learn and I'm not fully there yet!
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post #6 of 28 (permalink) Old 03-03-2017, 04:23 AM Thread Starter
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I'm beginning to get some readings as I get bit better at using the gizmo.
I am only working the 20 long for the first go at readings in various parts of the tank. One reason for that is that I totally screwed the build. I cut the wood to fit but then lost some of the length when adding the pen, extra length to keep me from sticking the probe in the substrate and adding the switch. Big DUMMY move as the switch goes in the water before I get the probe to the bottom of the 75!! No harm to the switch but it certainly messes with the PH reading.

On the 20, I'm still doing readings at various times in 6 points around the tank to try to get a few of the normal wrinkles ironed out. I assume there is a certain amount of error involved with any reading so I don't want to jump too far when I get what looks like a small change from point to point. I'm liking the way I can see the PH drops as the CO2 comes on and then settles but after it settles, I'm not sure I want to believe the readings. I'm taking three readings along the top and three down near the bottom. What has me guessing is that I see a .1 lower PH on all three bottom readings. Not enough info yet but then I would not expect more CO2 near the bottom than top surface.
More testing needed. Is .1 a significant difference or am I just seeing a consistent error?
I will study this before making any bold statements that my tank is that well fed.
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post #7 of 28 (permalink) Old 03-03-2017, 11:47 AM
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Yes I would think you would get a lower reading at the top and not the bottom also. I'll be watching for more results from your experimentation, as I have the same pen with the box.

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post #8 of 28 (permalink) Old 03-03-2017, 03:26 PM Thread Starter
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My readings are arranged and numbered left, center, and right as 1,2, and 3, with 4, 5, 6, going back along the right, center and left of the front glass.
This morning with the CO2 just beginning to work, the readings are moving off the normal tap of 7.9 but I do get the surprising slightly lower level at the bottom, rather than top.



I'm finding 1,2,3, and 6 are at 7.7 while 4, 5 are at 7.6. Again, whether this is real or just a slight glitch is not known but just another point where the lower reading ( higher CO2?) is down at the bottom.
Smallish tank with little plant or décor to distort the flow but seems an odd place for CO2 to be higher.
Some tank info? This is a tank that is in front of a window to get the stronger light as I use the obvious algae in other tanks for my African cichlid algea eating types. Not a tank designed for appearance but one of function where I can play things around easier than in large tanks.


Fish are 14 Protomelas insignus and 7 yellow labs as a growout group. Plants are a pretty random group. Some that was supposed to be anacharis , which I suspect may truly be hydrila but it was free and grows easy, some red murio and a sprig of java fern which broke off somewhere so got tucked under the rock. It is making the decision of whether it wants to stay or go?
A single rock pile for the comfort of the labs to get under, but no other décor. Equipment is an AC 30 HOB in the center back, a small surface skimmer on the right end . The CO2 enters through a small Grigg's style reactor (about 8" of 3/4 PVC pipe) powered by a Zoomed 501 filter. The output enters pointed toward the left end with no bubbles showing. I hate bubbles! Sub strate is a random combo of various sand, some Flourite red and varied amounts of yard dirt which gets spilled out of pots at times.
So with that much "stir" it seems the water should be pretty uniform at all points but then that is the point of the testing, measuring game, right?
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post #9 of 28 (permalink) Old 03-03-2017, 04:59 PM
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The only quote unquote dead spot If I were to guess would be position 4 where co2 would be trapped, but that does not explain position 5 because of the AC 30. My other question would be can co2 get trapped, besides in a cave like structure maybe. I notice that when I check the ph with my pen and just hold it still at the top of course it will read lets just say for example 7.6 but when I move it back and forth just a couple of inches it will change 0.1 point and stay there. Is that 0.1 point that much of a difference or that accurate with this type of pen? I DON'T KNOW. So what you could be measuring is maybe non existent, again I don't know.

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post #10 of 28 (permalink) Old 03-03-2017, 05:17 PM
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This is not my field of expertise, but could the depth/pressure affect the reading at 18"as apposed to at the surface?

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post #11 of 28 (permalink) Old 03-03-2017, 08:28 PM Thread Starter
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Good ideas and not something I can say so I'm going to take some readings and see how consistent they stay and if it is enough to matter at all. More a deal where I don't know, so want to find out?
For the depth question, I tend to think not on this tank as it is only a 12" deep for a 20 long. The increase in pressure is only .433PSI per foot so I might guess that would get us very little difference in the CO2 content? Not sure of that at this point, though.

Some readings taken at 3 PM are interesting as they tend to be consistent with the early readings.
From point 1 to 3 which are all across the top, the readings are 7.4, 7.2 and 7.1. the surprise there is that the end where the CO2 comes out of the tubing is the highest at 7.4 while the far end is 7.1.
But even more surprise for me, is that the bottom three all read 7.0.
My thought might have been that the CO2 would be stronger causing lower readings nearer the surface as it drifts upward.
Perhaps it is totally opposite and the surface is losing the CO2 faster, while it is staying down at the bottom where it is less prone to gassing off?

Last edited by PlantedRich; 03-03-2017 at 08:30 PM. Reason: correct typos
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post #12 of 28 (permalink) Old 03-03-2017, 11:43 PM
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Good ideas and not something I can say so I'm going to take some readings and see how consistent they stay and if it is enough to matter at all. More a deal where I don't know, so want to find out?
For the depth question, I tend to think not on this tank as it is only a 12" deep for a 20 long. The increase in pressure is only .433PSI per foot so I might guess that would get us very little difference in the CO2 content? Not sure of that at this point, though.

Some readings taken at 3 PM are interesting as they tend to be consistent with the early readings.
From point 1 to 3 which are all across the top, the readings are 7.4, 7.2 and 7.1. the surprise there is that the end where the CO2 comes out of the tubing is the highest at 7.4 while the far end is 7.1.
But even more surprise for me, is that the bottom three all read 7.0.
My thought might have been that the CO2 would be stronger causing lower readings nearer the surface as it drifts upward.
Perhaps it is totally opposite and the surface is losing the CO2 faster, while it is staying down at the bottom where it is less prone to gassing off?
The last statement makes sense to me.

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post #13 of 28 (permalink) Old 03-04-2017, 02:30 PM Thread Starter
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The last statement makes sense to me.

Now that I see it better, it really does make sense, just not the way I might have been thinking before. I was normally thinking that CO2 would drift up and out more than leaving it higher at the bottom while it dissipates higher.
Too many small points that I've never looked closely to see ?
Interested in seeing how it works in tanks with diffusers where we see the CO2 bubbles shooting straight up. Does the bottom contain more CO2 or is it more like my first impression?
Does more thorough diffusion change the picture?
At some point, when I get a better understanding of how the CO2 moves in the smaller, less complex tank, I will then move on to see what's up with the larger tanks where I expect it to be more difficult to sort out how the swirls and eddies of current may change the readings.
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post #14 of 28 (permalink) Old 03-04-2017, 09:35 PM
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Interested in seeing how it works in tanks with diffusers where we see the CO2 bubbles shooting straight up.

In my mind I always thought of co2 as like a bunch of helium balloons that we all try to keep in our tanks as long as possible to brush by the plants so that they get some benefit from it, weird I know but at any rate like you I hate seeing a bunch of tiny bubbles in my tank. I do believe the better the infusion the longer co2 remains in our tanks, microscopic bubbles would take longer to work their way up to the surface versus bigger ones and microscopic bubbles would have a much harder time fighting against any current or eddies. Look at what your doing to my mind... pretty soon I can picture myself lying in bed in the wee hours of the morning contemplating these things. lol

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post #15 of 28 (permalink) Old 03-05-2017, 12:17 AM Thread Starter
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I spend a lot of time just waiting around for things to move so I spend a lot of time just on the forum. That is one thing that leads me to wander into the fish room and change up the mind a bit with things that I never considered.
Sorry, if I'm leading you along as it may be a really tangled trip!
I have not even started on looking at the larger tanks which should really be more difficult with all the different currents around plants, rock piles and such.
I have finally gotten enough of the ucky puck on all the holes in the box. I was get afraid to stick it in the water because I found a new hole every time I went deep.
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